Method for estimating and improving current sampling precision by using temperature of shunt

Abstract

The invention discloses a method for improving current sampling precision through shunt temperature estimation, and the method comprises the following steps: S1, building a second-order equivalent thermal impedance model through the cavity temperature and loss power of a shunt, and obtaining an actual temperature value of the shunt; s2, obtaining actual resistance values at different resistance temperatures according to a conversion formula of the resistance values at different temperatures; and S3, converting a voltage signal actually acquired by the DSP into an actual current value. The method has the advantages of being simple in principle, convenient to operate, high in metering precision and the like, current precision of the shunt can be improved through thermal simulation and test correction, dependence on divider resistance precision of a hardware sampling circuit is reduced, the number of components in the hardware sampling circuit is reduced, hardware cost is saved, and PCB space is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of current sampling control, and in particular to a method for improving current sampling accuracy by estimating shunt temperature. Background Art

[0002] With the continuous improvement of on-board power supply technology for new energy vehicles, the control accuracy requirements for output current are getting higher and higher, and the cost requirements are strict. During the full-scale data measurement process of products based on shunts for current measurement, the measurement accuracy will be affected by the following factors: 1) The resistance error caused by the shunt itself and the assembly welding process; 2) The resistance change error of the shunt at different temperatures; 3) The resistance change error of the shunt under different load current conditions. Therefore, in the scenario where the shunt is used as a current sampling sensor, how to improve the current sampling accuracy poses a challenge. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for improving current sampling accuracy by using shunt temperature estimation, which has simple principle, convenient operation and high sampling accuracy, in view of the deficiencies in the prior art.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A method for improving current sampling accuracy by using shunt temperature estimation comprises the following steps:

[0006] Step S1, establishing a second-order equivalent thermal impedance model through the shunt cavity temperature and power loss to obtain the actual temperature value of the shunt;

[0007] Step S2, obtaining actual resistance values ​​at different resistance temperatures according to the conversion formula of resistance values ​​at different temperatures;

[0008] Step S3: converting the voltage signal actually collected by DSP into an actual current value.

[0009] As a further improvement of the present invention, in step S2, the conversion relationship of the resistance value is:

[0010] R t =R0*(1+k*(t-t0))---(Formula 1)

[0011] Among them, R t is the resistance value at temperature t, R0 is the resistance value at temperature t0, and k is the resistance temperature coefficient.

[0012] As a further improvement of the present invention, in step S3, the actual current value I o Calculated by (Formula 2):

[0013]

[0014] Among them, I o is the actual current value after correction, a is the sampling circuit conversion coefficient, V ADC is the analog-to-digital conversion value.

[0015] As a further improvement of the present invention, in step S1, the thermal impedance model includes resistor R1, resistor R2, capacitor C1 and capacitor C2, resistor R1 / capacitor C1 and resistor R2 / capacitor C2 form a second-order network, and the second-order network is set to an overall impedance Zth, Ploss is used as the power loss on the shunt, which is equivalent to the current source in the thermal impedance model, the shunt cavity temperature Tc is equivalent to the voltage source of the thermal impedance model, Ta is the actual temperature of the shunt, therefore, the actual shunt temperature Ta=Tc+δT, wherein δT is the temperature rise value of the shunt.

[0016] As a further improvement of the present invention, in the thermal impedance model, the overall impedance Zth is composed of two first-order inertia links superimposed, and the overall impedance Zth satisfies the relationship shown in (Formula 3):

[0017]

[0018] Where Ploss = I 2 R, Ploss is the power loss, I is the sampling current, and R is the standard resistance value of the shunt.

[0019] As a further improvement of the present invention, a Laplace transform is performed on (Formula 3) to obtain a transfer function G(s) with an input of Ploss and an output of δT, as shown in (Formula 4):

[0020]

[0021] Where τ = RC;

[0022] The transfer function G(s) is converted into the sum of two low-pass filters in parallel, as shown in (Formula 5):

[0023]

[0024] Where τ = RC, T s is the sampling period;

[0025] therefore,

[0026] δT=y(n)*Ploss

[0027] T a =δT+T c ---(Formula 6)

[0028] Substituting (Formula 6) into (Formula 1) and (Formula 2) can obtain the corrected current value.

[0029] Compared with the prior art, the advantages of the present invention are:

[0030] The method of improving current sampling accuracy by using shunt temperature estimation of the present invention can improve the shunt current accuracy through thermal simulation and experimental correction, reduce the dependence on the accuracy of the voltage divider resistor of the hardware sampling circuit, simplify the number of components in the hardware sampling circuit, save hardware costs, and reduce PCB space. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structural principle of the thermal impedance model in a specific embodiment of the present invention;

[0032] Figure 2 It is a flow chart of improving the current sampling accuracy by using the shunt temperature estimation in a specific embodiment of the present invention; DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0034] In the description of the present invention, it should be understood that the terms "side", "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 invention 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 limiting the present invention.

[0035] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or suggesting 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 one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0036] Example

[0037] like Figure 1 and Figure 2 As shown, the method of improving current sampling accuracy by using shunt temperature estimation of the present invention comprises the following steps:

[0038] Step S1, establishing a second-order equivalent thermal impedance model through the shunt cavity temperature and power loss to obtain the actual temperature value of the shunt;

[0039] Step S2, obtaining actual resistance values ​​at different resistance temperatures according to the conversion formula of resistance values ​​at different temperatures;

[0040] Step S3: convert the voltage signal actually collected by DSP (microcontroller chip) into an actual current value.

[0041] In step S2, the conversion relationship of the resistance value is:

[0042] R t =R0*(1+k*(t-t0))---(Formula 1)

[0043] Among them, R t is the resistance value at temperature t, R0 is the resistance value at temperature t0, and k is the resistance temperature coefficient.

[0044] In step S3, the actual current value I o Calculated by (Formula 2):

[0045]

[0046] Among them, I o is the actual current value after correction, a is the sampling circuit conversion coefficient, V ADC is the analog-to-digital conversion value.

[0047] In step S1, the thermal impedance model includes resistor R1, resistor R2, capacitor C1 and capacitor C2. Resistor R1 / capacitor C1 and resistor R2 / capacitor C2 form a second-order network, and the second-order network is set to an overall impedance Zth. Ploss is used as the power loss on the shunt, which is equivalent to the current source in the thermal impedance model. The shunt cavity temperature Tc is equivalent to the voltage source of the thermal impedance model. Ta is the actual temperature of the shunt. Therefore, the actual shunt temperature Ta=Tc+δT, where δT is the temperature rise value of the shunt.

[0048] In actual circuit applications, the real-time temperature t on the resistor cannot be directly obtained, but the shunt cavity temperature (Tc) in the actual product is relatively easy to obtain through the NTC sampling resistor. In addition, during product operation, the power loss Ploss on the shunt can be obtained. In this embodiment, a second-order equivalent thermal impedance model is established through the cavity temperature (Tc) and the power loss Ploss. This thermal impedance model is corrected through simulation combined with actual testing to obtain the actual shunt temperature, and the real resistance is obtained according to (Formula 1), and then the real current value is obtained through (Formula 2).

[0049] In this embodiment, the improvement of current sampling accuracy is mainly reflected in that the actual temperature of the shunt is estimated by the thermal impedance model at different resistance temperatures, and then the actual resistance of the shunt is corrected by (Formula 1), and then the actual sampling current is obtained according to (Formula 2). Since the influence of temperature on the impedance characteristics of the shunt is taken into account in principle, the current sampling accuracy at different resistance temperatures is improved.

[0050] In the thermal impedance model, the overall impedance Zth is composed of two first-order inertia links, and the overall impedance Zth satisfies the relationship shown in (Formula 3):

[0051]

[0052] Where Ploss = I 2 R, Ploss is the power loss, I is the sampling current, and R is the standard resistance value of the shunt.

[0053] Furthermore, by performing Laplace transform on (Formula 3), a transfer function G(s) with input Ploss and output δT is obtained, as shown in (Formula 4):

[0054]

[0055] Where, τ = RC;

[0056] The transfer function G(s) is converted into the sum of two low-pass filters in parallel, as shown in (Formula 5):

[0057]

[0058] Where τ = RC, T s is the sampling period;

[0059] therefore,

[0060] δT=y(n)*Ploss

[0061] T a =δT+T c ---(Formula 6)

[0062] Substituting (Formula 6) into (Formula 1) and (Formula 2) can obtain the corrected current value.

[0063] In this embodiment, the shunt current accuracy can be improved through thermal simulation and experimental correction, which reduces the dependence on the accuracy of the voltage divider resistor of the hardware sampling circuit, simplifies the number of components in the hardware sampling circuit, saves hardware costs, and reduces PCB space.

[0064] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for improving current sampling accuracy by using shunt temperature estimation, characterized in that: The following steps are involved: Step S1, establishing a second-order equivalent thermal impedance model through the shunt cavity temperature and power loss to obtain the actual temperature value of the shunt; Step S2, obtaining actual resistance values ​​at different resistance temperatures according to the conversion formula of resistance values ​​at different temperatures; Step S3: converting the voltage signal actually collected by DSP into an actual current value.

2. The method for improving current sampling accuracy by using shunt temperature estimation according to claim 1, characterized in that: In step S2, the conversion relationship of the resistance value is: R t =R0*(1+k*(t-t0))---(Formula 1) Among them, R t is the resistance value at temperature t, R0 is the resistance value at temperature t0, and k is the resistance temperature coefficient.

3. The method for improving current sampling accuracy by using shunt temperature estimation according to claim 2, characterized in that: In step S3, the actual current value I o Calculated by (Formula 2): Among them, I o is the actual current value after correction, a is the sampling circuit conversion coefficient, V ADC is the analog-to-digital conversion value.

4. The method for improving current sampling accuracy by using shunt temperature estimation according to claim 3, characterized in that: In the step S1, the thermal impedance model includes resistor R1, resistor R2, capacitor C1 and capacitor C2, resistor R1 / capacitor C1, resistor R2 / capacitor C2 form a second-order network, and the second-order network is set to an overall impedance Zth, Ploss is used as the power loss on the shunt, which is equivalent to the current source in the thermal impedance model, the shunt cavity temperature Tc is equivalent to the voltage source of the thermal impedance model, Ta is the actual temperature of the shunt, therefore, the actual shunt temperature Ta=Tc+δT, wherein δT is the temperature rise value of the shunt.

5. The method for improving current sampling accuracy by using shunt temperature estimation according to claim 4, characterized in that: In the thermal impedance model, the overall impedance Zth is composed of two first-order inertia links superimposed, and the overall impedance Zth satisfies the relationship shown in (Formula 3): Where Ploss = I 2 R, Ploss is the power loss, I is the sampling current, and R is the standard resistance value of the shunt.

6. The method for improving current sampling accuracy by using shunt temperature estimation according to claim 5, characterized in that: By performing Laplace transform on (Formula 3), we can obtain the transfer function G(s) with input Ploss and output δT, as shown in (Formula 4): Where, τ = RC; The transfer function G(s) is converted into the sum of two low-pass filters in parallel, as shown in (Formula 5): Where τ = RC, T s is the sampling period; therefore, δT=y(n)*Ploss T a =δT+T c ---(Formula 6) Substituting (Formula 6) into (Formula 1) and (Formula 2) can obtain the corrected current value.

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