Double-sided interactive temperature compensation leakage protection sensor and temperature compensation method

Abstract

The present invention belongs to the field of residual current sensors, and particularly relates to a double-sided interactive temperature-compensated leakage protection sensor and a temperature compensation method. The sensor is composed of an electromagnetic conversion component, a main acquisition board, and a signal polarity conversion switch. The electromagnetic conversion component is isolated from the entire system, and other circuit units are placed together. The total temperature drift error is equal to the temperature drift error of the electromagnetic conversion component + the total error of the main acquisition board. Compared with the existing technology, the present invention does not require the generation of a temperature compensation curve table, greatly improving the production efficiency of the sensor. The sensor is also very simple to implement: in terms of hardware, only a set of double-connected double-open relays or low-on-resistance analog switches need to be added to the original single-sided sensor, and the circuit can interchange coils through two sets of bridge-type tubes. The measurement accuracy is greatly improved because part of the temperature drift of the PCBA and the power supply voltage drift are offset.

Description

Technical Field

[0001] The present invention relates to a residual current sensor, and more particularly to a double-sided interactive temperature compensation leakage protection sensor and a temperature compensation method. Background Art

[0002] Residual current sensors are often used outdoors in applications such as car charging stations, photovoltaic power generation, on-board OBC, and charging cables. Due to the large temperature difference outdoors, the sensor temperature drift is more serious. In the north, the temperature may reach -20 or even 40 degrees Celsius at night, and in some places, the temperature exceeds 100 degrees Celsius under the scorching sun in the afternoon. The zero point of the sensor at different temperatures will drift with the change of temperature. When the sensor is required to detect protection functions below 10 mA, these temperature drift errors become more serious.

[0003] The existing temperature compensation method of residual current sensor is: it memorizes the zero point position at different temperatures and generates a table - temperature compensation curve table (such as Figure 1 As shown in the temperature curve table of NTC, the compensation principle is as follows:

[0004] Assuming the current temperature Ci is -26°C, the algorithm for estimating the current temperature zero point value is to subtract the voltage V3 corresponding to the next temperature from the voltage V4 corresponding to the previous temperature range. Then V4-V3 is the temperature-voltage drift coefficient K corresponding to the temperature range between -25°C and -30°C. Therefore, K3=(V4-V3) / 5°C. That is, between -30°C and -25°C, the corresponding temperature drift voltage is K3 for every 1°C increase in temperature.

[0005] Therefore, the estimated zero-point voltage Vzero is: Vzero=(Ci-V3)*K3+V3, that is, the voltage corresponding to the next temperature range is used as the benchmark to increase the approximately linear voltage difference in this section. In other words, although the overall temperature drift coefficient is a curve, it can be approximated as a straight line under small temperature differences.

[0006] In order to obtain the temperature corresponding to the voltage table at zero current, the following method is used:

[0007] 1) Before leaving the factory, the tooling board is inserted into the high and low temperature box and powered on. Generally, one tooling board can hold 50 pieces, and one furnace can hold 200 pieces. It can be done together with the glue baking, but the low temperature zone cannot be done together with the glue baking, which will result in low production efficiency;

[0008] 2) Provide a temperature curve table that is consistent with most sensors. The disadvantage is that many individual sensors will not meet the accuracy requirements and will be considered defective.

[0009] 3) During use, under the premise of knowing that there is no current, the zero point value is memorized according to the ambient temperature (such as during the self-test process, the circuit will not be powered). The disadvantage is that the parameters need to be memorized slowly, and the temperature points that are not memorized cannot be compensated.

[0010] Therefore, it is not easy to obtain this temperature compensation table. And because the individual sensors are very different, it is basically necessary to generate a table for each sensor according to its own individual characteristics.

[0011] In addition, due to factors such as power supply voltage and component position movement, the entire temperature drift curve will shift and no longer apply. Summary of the Invention

[0012] In view of the deficiencies in the prior art, the object of the present invention is to provide a double-sided interactive temperature compensation leakage protection sensor and a temperature compensation method that solve the above technical problems.

[0013] To achieve the above object, the present invention provides the following technical solutions:

[0014] The double-sided interactive temperature compensation leakage protection sensor is characterized by including

[0015] The electromagnetic conversion component includes a measured conductor, a magnetic ring, and an oscillation excitation coil. The measured conductor corresponds to the magnetic ring, and the oscillation excitation coil is wound around the magnetic ring. The magnetic ring includes a positive surface A and a negative surface B.

[0016] The main acquisition board is used for current signal acquisition, amplification, filtering and data processing on the positive side A and the negative side B.

[0017] Signal polarity conversion switch, used to switch the current signal direction between the positive side A and the negative side B.

[0018] Furthermore, the main acquisition board includes a 2.5V reference power supply module, a square wave oscillator, a signal processing module and an MCU module. The signal processing module is used to filter out the oscillation wave of the current signal and restore it to the measured current waveform. The MCU module is used to collect and process the current signal. The square wave oscillator is used to amplify the current signal. The main acquisition board is a PCBA circuit board.

[0019] Furthermore, the signal polarity conversion switch is connected to the oscillation excitation coil and the main acquisition board, and the MCU module controls the signal polarity conversion switch to switch the current signal direction of the positive side A and the negative side B.

[0020] The double-sided interactive temperature compensation method includes an electromagnetic conversion component, a main acquisition board, and a signal polarity conversion switch. The electromagnetic conversion component is separated from the entire system, and other circuit units are placed together. The total temperature drift error is equal to the temperature drift error of the electromagnetic conversion component + the total error of the main acquisition board.

[0021] The MCU module of the main acquisition board controls the signal polarity conversion switch to switch to the positive side A to first collect the current signal and perform the DC component of the current in one direction; then controls the signal polarity conversion switch to switch to the negative side B to collect the DC component of the current in the opposite direction, and quickly switches and collects between the two directions.

[0022] Furthermore, the switch is controlled to connect the positive side A. Assuming that the feedback signal is greater than the 2.5V reference after amplification and filtering, it is a positive current. At this time, the positive current is integrated to obtain a stable DC component IA.

[0023] Control the switch and connect the negative side B, which is actually still the A side, but the direction of the excitation square wave and the direction of the feedback signal are switched. Then, after the feedback signal is amplified and filtered, a current IB in the opposite direction will appear.

[0024] (IA-IB) / 2 is approximately equal to the value of the measured current, which has offset most of the temperature drift error of the main acquisition board.

[0025] Furthermore, when the zero-point parameter calibration and gain parameter calibration are performed on the positive side A, the temperature is T1. At the temperature T2, a residual DC current Is is measured, and the current-voltage conversion coefficient is R. The gain deviation at this time is a%, that is, the residual current conversion output voltage Va of the A side is Va=Is*(1+a%)*R+Vref; the conversion component now produces a positive error of a%. Since the value of a% cannot be determined, the zero-point voltage Vref cannot be calculated, and only the conversion output voltage Va can be obtained.

[0026] Furthermore, zero-point and gain calibrations are performed on surface B at the same temperature T1. At temperature T2, a residual DC current (Is) is measured. Similarly, the current-to-voltage conversion coefficient is R, and the gain loss is a%. Because the control signal polarity conversion switch is switched to the negative surface B, the output signal of the measured signal is reversed after passing through the electromagnetic conversion component. Since the direction of the measured wire through the magnetic core remains unchanged, the output signal voltage amplitude of the electromagnetic conversion component remains unchanged. The direction of the temperature drift error and the direction of the signal are both reversed. The electromagnetic conversion component outputs Isample = Is*(1+ a%)mA, which is reversed to Isample = -Is*(1+ a%)mA. Therefore, the B-surface residual current conversion output voltage Vb = -Is*(1+ a%)*R+Vref.

[0027] Through the equation:

[0028] ①Va=Is*(1+ a%)*R+Vref;

[0029] ②Vb= -Is*(1+ a%)*R+Vref;

[0030] Since Va and Vb are collected values, Vref is the zero point after temperature drift;

[0031] Va+Vb=2*Vref, so Vref=(Va+Vb) / 2;

[0032] Finally, the zero point Vref and the measured current I after temperature drift are obtained.

[0033] By adopting the above technical solution, the beneficial effects of the present invention are:

[0034] 1. No need to generate temperature compensation curve table, the production efficiency of the sensor is greatly improved.

[0035] 2. The implementation of the sensor is also very simple: in terms of hardware, it is only necessary to add a set of double-connected double-open relays or low-on-resistance analog switches on the basis of the original single-sided sensor, and the circuit can interchange coils through two sets of bridge tubes.

[0036] 3. The measurement accuracy has been greatly improved due to the offset of part of the PCBA temperature drift and power supply voltage drift. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Temperature compensation curve tables generated for existing residual current sensors.

[0038] Figure 2 Schematic diagram of the model structure of an embodiment of the present invention.

[0039] Figure 3 2 is a circuit diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0042] like Figure 2 and Figure 3 As shown in the figure, the sensor consists of an electromagnetic conversion component, a main acquisition board, and a signal polarity conversion switch. The electromagnetic conversion component is separated from the entire system, and other circuit units are placed together. The total temperature drift error is equal to the temperature drift error of the electromagnetic conversion component + the total error of the main acquisition board.

[0043] The electromagnetic conversion component includes a measured conductor, a magnetic ring, and an oscillation excitation coil. The magnetic ring includes a positive side A and a negative side B. The main acquisition board includes a 2.5V reference power supply module, a square wave oscillator, a signal processing module, and an MCU module. The MCU module of the main acquisition board controls the signal polarity conversion switch to switch to the positive side A to first collect the current signal and perform the DC component of the current in one direction; then controls the signal polarity conversion switch to switch to the negative side B to collect the DC component of the current in the opposite direction, and quickly switches and collects between the two directions.

[0044] The temperature drift compensation principle algorithm is as follows:

[0045] 1) First of all, the DC acquisition error is composed of multiple parts: electromagnetic conversion components, power supply voltage driving the main acquisition board, 2.5V reference voltage, feedback resistor temperature drift, op amp offset voltage sensitivity at different temperatures, ADC acquisition temperature drift, etc.

[0046] 2) Then, based on the temperature errors of these components, separate them and reassemble the separable parts as shown in the structure diagram above: the electromagnetic conversion component is separated from the entire system, and the other circuit units are put together. The total temperature drift error is then equal to: the temperature drift error of the electromagnetic conversion component + the total error of the PCBA circuit board. Because the PCBA includes a large number of signal processing units, oscillation drivers, and power supply circuits, the PCBA also separates the majority of the temperature drift error. Therefore, by finding a way to eliminate or reduce the interference caused by the PCBA error on the measurement, the impact of the overall temperature drift on the acquisition accuracy can be reduced.

[0047] 3) Assuming the factory performs zero-point and gain calibration at 20°C, and measures a 10mA (true value) DC current at 30°C, the gain loss is 0.1%, meaning the 10mA acquisition value is only 9.99mA. The electromagnetic conversion component generates a positive error of 0.2mA, and the PCBA generates a positive error of 1.5mA. Therefore, the acquired current value, I, = 0.2mA + 1.5mA + 9.99mA = 11.69mA. The total error is 11.69-10 = 1.69mA, a 16.9% error. While we can achieve an error of less than 5% from -20°C to +85°C with single-sided acquisition, we cannot achieve the same accuracy as a dual-sided complementary solution.

[0048] 4) Under the same conditions as above, the measured value of I-Cai = 0.2mA + 1.5mA + 9.99mA = 11.69mA. The MCU then controls switch k1 on the AB side, switching from A to B. As a result, the measured signal's output is reversed after electromagnetic conversion. Since the direction of the measured wire through the magnetic core remains unchanged, the output signal voltage amplitude of the electromagnetic conversion component remains unchanged. The direction of the temperature drift error and the direction of the signal are both reversed, resulting in the measured value of I-Cai = -0.2mA + 1.5mA - 9.99mA. This means that the 10mA output of the electromagnetic conversion component is reversed to -10mA, and then attenuated by 0.1% in the acquisition and amplification circuitry to -9.99mA. The 0.2mA temperature drift of the electromagnetic conversion component is reversed to -0.2mA. However, the PCBA's temperature drift, caused by drift in the power supply and reference voltage, does not change direction, but rather increases or decreases overall, remaining at +1.5mA.

[0049] Therefore, by simply adding the forward I sampling + the reverse I sampling, we can get the PCBA's temperature drift current = [(0.2mA + 1.5mA + 9.99mA) + (- 0.2mA + 1.5mA - 9.99mA)] / 2 = 1.5mA. Once the PCBA's temperature drift is calculated, the above formula = 1.5mA, and then the test value of side A (11.69mA - 1.5mA = 10.19) is subtracted. The error becomes (10.19-10) / 10 = 1.9%, which is much more accurate than the 16.9% error mentioned above.

[0050] 5) In addition, (IA - IB) / 2 is approximately equal to the value of the measured current. The temperature drift of the PCBA can be directly eliminated to calculate: Measured current I = [(0.2mA + 1.5mA + 9.99mA) - (- 0.2mA + 1.5mA - 9.99mA)] / 2 = (0.4 + 19.98) / 2 = 10.19mA. The temperature drift of the electromagnetic conversion component and the loss of the PCBA's amplification factor are still present, but the overall temperature drift error of the PCBA's zero axis, which is increased or decreased, is eliminated.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. Double-sided interactive temperature compensation leakage protection sensor, characterized in that: include The electromagnetic conversion component includes a measured conductor, a magnetic ring, and an oscillation excitation coil. The measured conductor corresponds to the magnetic ring, and the oscillation excitation coil is wound around the magnetic ring. The magnetic ring includes a positive surface A and a negative surface B. The main acquisition board is used for current signal acquisition, amplification, filtering and data processing on the positive side A and the negative side B. Signal polarity conversion switch, used to switch the current signal direction between the positive side A and the negative side B; The main acquisition board includes a 2.5V reference power supply module, a square wave oscillator, a signal processing module and an MCU module. The signal processing module is used to filter the oscillation wave of the current signal and restore it to the measured current waveform. The MCU module is used to collect and process the current signal. The square wave oscillator is used to convert the residual current signal into a voltage signal. The main acquisition board is a PCBA circuit board. The signal polarity conversion switch is connected to the oscillation excitation coil and the main acquisition board, and the MCU module controls the signal polarity conversion switch to switch the current signal direction of the positive side A and the negative side B.

2. The temperature compensation method implemented by the temperature compensation leakage protection sensor according to claim 1 is characterized in that: Including electromagnetic conversion components, main acquisition board and signal polarity conversion switch, and the electromagnetic conversion components are separated from the entire system, and other circuit units are put together. The total temperature drift error is equal to the temperature drift error of the electromagnetic conversion component + the total error of the main acquisition board; The MCU module of the main acquisition board controls the signal polarity conversion switch to switch to the positive side A to first collect the current signal and perform the DC component of the current in one direction; then controls the signal polarity conversion switch to switch to the negative side B to collect the DC component of the current in the opposite direction, and quickly switches and collects between the two directions.

3. The temperature compensation method according to claim 2, characterized in that: Control the switch and connect the positive side A. Assuming that the feedback signal is greater than the 2.5V reference after amplification and filtering, it is a positive current. At this time, the positive current is integrated to obtain a stable DC component IA. Control the switch and connect the negative side B, which is actually still the A side, but the direction of the excitation square wave and the direction of the feedback signal are switched. Then, after the feedback signal is amplified and filtered, a current IB in the opposite direction will appear. (IA-IB) / 2 is approximately equal to the value of the measured current, which has offset most of the temperature drift error of the main acquisition board.

4. The temperature compensation method according to claim 3, wherein: When the zero-point parameter calibration and gain parameter calibration are performed on the positive side A, the temperature is T1. At the temperature T2, a residual DC current Is is measured, and the current-voltage conversion coefficient is R. The gain deviation at this time is a%, that is, the residual current conversion output voltage Va of the A side is Va=Is*(1+a%)*R+Vref; the electromagnetic conversion component now produces a positive error of a%. Since the value of a% cannot be determined, the zero-point voltage Vref cannot be calculated, and only the conversion output voltage Va can be obtained.

5. The temperature compensation method according to claim 4, characterized in that: Perform zero-point and gain calibration on surface B at the same temperature T1. Measure the residual DC current Is at temperature T2, using the same current-to-voltage conversion factor R. The gain loss is a%. Because the control signal polarity switch is switched to the negative surface B, the output signal of the measured signal is reversed after passing through the electromagnetic conversion component. Since the direction of the measured wire through the magnetic core remains unchanged, the output signal voltage amplitude of the electromagnetic conversion component remains unchanged. The direction of both the temperature drift error and the signal is reversed. The electromagnetic conversion component's output voltage, I = Is * (1 + a%) mA, is reversed to I = - Is * (1 + a%) mA. Therefore, the B-surface residual current conversion output voltage, Vb, is - Is * (1 + a%) * R + Vref. Through the equation: ①Va=Is*(1+ a%)*R+Vref; ②Vb= -Is*(1+ a%)*R+Vref; Since Va and Vb are collected values, Vref is the zero point after temperature drift; Va+Vb=2*Vref, so Vref=(Va+Vb) / 2; Finally, the zero point Vref and the measured current I after temperature drift are obtained.

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