Detection circuit for alternating current containing harmonic waves and adjustment and calibration method thereof

Abstract

A detection circuit for alternating current containing harmonic waves comprises a Hall current sensor used for collecting input current and converting the input current into Hall potential signals to be output; the high-pass filter circuit is used for filtering zero-current bias voltage in the Hall potential output by the Hall current sensor and retaining an alternating-current voltage signal; the reverse amplification circuit is used for amplifying the AC voltage signal received by the inverted input end and outputting the amplified voltage signal; the direct current bias circuit is used for providing an adjustable direct current bias voltage signal for the alternating current voltage signal amplified by the reverse amplification circuit; and the analog-to-digital converter is used for converting the received amplified voltage signal and the direct current bias voltage signal into digital signals, and then comparing the two signals to calculate the current value ix output to be measured. The bias voltage converted by the Hall current sensor can be output, and the measurement precision is effectively improved.

Description

Technical Field

[0001] The invention relates to a detection circuit for harmonic alternating current and a calibration method thereof, which are specifically suitable for reducing measurement errors and improving measurement accuracy. Background Art

[0002] The current power grid contains a large number of power electronic equipment, and the grid current contains a lot of harmonics, especially when the grid fails, the harmonic content in the fault current is even richer. If the traditional current transformer is used for AC current detection, because the bandwidth of the current transformer is very narrow, the general current transformer can only accurately measure the AC current of about 50Hz. For harmonics with a frequency higher than 50Hz, the current transformer measurement error is large.

[0003] Hall current sensors can be used to measure AC currents, and their bandwidth can reach tens of kHz. Some Hall current sensors can reach 1MHz. Currents from 0Hz to several kHz are within the measurement range of Hall current sensors. Figure 5 , is an existing current detection circuit composed of Hall current sensors, wherein U1 is a Hall current sensor, assuming that the current to be measured is i, the current to be measured i may contain DC and AC components, the reference direction of the current to be measured i is flowing in from the positive input current pin IP+ of the Hall current sensor U1, and flowing out from the negative input current pin IP-, and the voltage of the output pin of the Hall current sensor U1 is represented by v o Indicates that v o The reference point is the voltage GND of the Hall current sensor ground pin. o I meet:

[0004] v o =v Q +K·i (1)

[0005] Where, the unit of i is ampere, i is a signed quantity, when i flows into the positive input current pin of the Hall current sensor, that is, the IP+ pin, it is positive, when i flows out of the positive input current pin of the Hall current sensor, that is, the IP+ pin, it is negative; v Q is the zero current output voltage of the Hall current sensor, that is, the output voltage v when the input current i is 0 o The value of v Q The unit of is volt; K is the current gain coefficient of the Hall current sensor, and the unit of K is ohm. Ideally, K is a constant.

[0006] In the existing current detection circuit composed of Hall current sensor, v in equation (1) is generally replaced by o Sent to the IN1 or IN2 pin of the ADC (analog-to-digital converter), the analog-to-digital conversion is used to obtain v oThe corresponding digital quantity. According to v o The corresponding digital quantity can be obtained as v o The value of i can be deduced from equation (1). Q and K are considered constants, and the v of many Hall current sensors Q There is no external output, that is, there is no dedicated pin to output V Q , is generally determined based on the value given in the Hall current sensor manual; K is also fixed and cannot be adjusted. Q is the zero current output voltage of the Hall current sensor, v Q The error is generally 1%-3%, and v Q It will change with the power supply voltage of the Hall current sensor, the current to be measured, the ambient temperature and other parameters; K is the current gain coefficient. The error of the current gain coefficient K of a well-made Hall current sensor will reach 2-5%, and the error of the current gain coefficient K of a general Hall current sensor will reach 5-15%. Therefore, due to v Q Due to the influence of these two parameters, the accuracy of the current detection circuit composed of the existing open-loop Hall current sensor is not high, and the error generally reaches 5%-15%.

[0007] Because v Q and K are not adjustable. Figure 5 The power supply voltage VC1 of the Hall current sensor U1 and the power supply voltage VC2 of the analog-to-digital converter need to match; if they do not match, the input voltage range of the analog-to-digital converter, that is, the measuring range, will not be fully utilized, which will also cause a decrease in accuracy.

[0008] In addition, because the models of Hall current sensors are not continuous, according to the maximum range of the measured current, the models of Hall current sensors on the market are generally divided into ±2.5A, ±5A, ±10A, ±20A, ±30A and other grades. If the maximum value of the current to be measured does not completely match the maximum range of the current measured by the Hall current sensor, the range of the analog-to-digital converter will not be fully utilized, resulting in reduced accuracy. Assuming that the maximum instantaneous value of the current to be measured is 3A, if a ±5A Hall current sensor is selected, the output voltage signal v of the Hall current sensor o The maximum voltage dynamic range within the positive and negative power rails cannot be achieved. o Sending it directly to the analog-to-digital converter will result in the analog-to-digital converter's range not being fully utilized. Summary of the invention

[0009] The purpose of the present invention is to Q The low-performance, low-precision Hall sensor with no external output is converted into a high-precision, v QCan be output externally, v Q AC current measurement circuit with independent adjustable K, thus avoiding the Q Not output, v Q The unadjustable K and K have an adverse effect on the measurement accuracy, thereby providing a detection circuit and a calibration method for harmonic AC current that can reduce measurement errors and improve measurement accuracy.

[0010] To achieve the above objectives, the technical solution of the present invention is:

[0011] In a first aspect, the present invention provides a detection circuit for harmonic AC current, comprising:

[0012] Hall current sensor, used to collect input current i x And converted into Hall potential signal v A Output;

[0013] The high-pass filter circuit is connected in series to the signal output terminal Vout of the Hall current sensor to filter out the zero current bias voltage v in the Hall potential output by the Hall current sensor. Q , retain the AC voltage signal v AS , v A =v Q +v AS , AC voltage signal v AS After passing through the high-pass filter circuit, the attenuated AC voltage signal v is obtained. BS ;

[0014] The reverse amplifier circuit has an inverting input terminal connected in series with a filter circuit to receive an attenuated AC voltage signal v at the inverting input terminal. BS Amplify and output the amplified voltage signal v D ;

[0015] The DC bias circuit is connected to the in-phase input terminal of the reverse amplifier circuit and is used to amplify the AC voltage signal v D Provides an adjustable DC bias voltage signal v N ;

[0016] The analog-to-digital converter has a first signal input terminal IN1 connected to the signal output terminal of the reverse amplifier circuit, and a second signal input terminal IN2 connected to the in-phase input terminal of the reverse amplifier circuit, and is used to receive the amplified voltage signal v D With the DC bias voltage signal v N Converted into digital signal Data_v D and Data_v N , and then compare the two signals to calculate the current value i to be measured x Output.

[0017] The high-pass filter circuit is an RC filter circuit formed by connecting a first capacitor C1 and a resistor R1 in series. The AC minimum attenuation rate β of the high-pass filter circuit is min =0.9999, then we can approximately assume that v BS＝ v AS ;

[0018] The reverse amplification circuit is obtained by connecting a first potentiometer R2 in parallel between the inverting input terminal and the signal output terminal of the first operational amplifier U3, and connecting a resistor R1 to the inverting input terminal of the first operational amplifier U3;

[0019] The high-pass filter circuit and the reverse amplifier circuit share a resistor R1;

[0020] The current value to be measured is

[0021] Where V c2 is the voltage value of the power supply VC2 of the analog-to-digital converter, n is the number of bits of the analog-to-digital converter conversion result, λ is the overall current gain coefficient of the circuit, K is the current gain coefficient of the Hall current sensor.

[0022] The resistor R1 and the first capacitor C1 satisfy the following relationship:

[0023]

[0024] In the above formula, β min is the minimum amplitude attenuation rate allowed by the high-pass filter circuit composed of the resistor R1 and the first capacitor C1, θ max is the maximum phase difference allowed by the output signal of the high-pass filter circuit relative to the input signal, ω min is the AC current i to be detected x The lowest angular frequency.

[0025] The DC bias circuit includes a second potentiometer R3 and a second capacitor C2, wherein two fixed terminals of the second potentiometer R3 are respectively connected to the power supply VC2 and the ground; a sliding terminal of the second potentiometer R3 is simultaneously connected to the in-phase input terminal of the reverse amplifier circuit and the second signal input terminal IN2 of the analog-to-digital converter;

[0026] The non-inverting input terminal of the reverse amplifier circuit is connected in series with a second capacitor C2 and then grounded.

[0027] The DC bias circuit includes a second potentiometer R3 and a second operational amplifier U4, wherein the two fixed terminals of the second potentiometer R3 are respectively connected to the power supply VC2 and the ground; the sliding terminal of the second potentiometer R3 is connected to the non-inverting input terminal of the second operational amplifier U4, the inverting input terminal of the second operational amplifier U4 is connected to the signal output terminal of the second operational amplifier U4, and the signal output terminal of the second operational amplifier U4 is simultaneously connected to the non-inverting input terminal of the reverse amplifier circuit and the second signal input terminal IN2 of the analog-to-digital converter.

[0028] The signal output terminal Vout of the Hall current sensor is connected in series with a third capacitor C3 and then grounded.

[0029] In a second aspect, the present invention provides a method for adjusting parameters of a detection circuit containing harmonic alternating current, comprising the following steps:

[0030] S1, adjust the DC bias voltage signal v N , so that v N =V c2 / 2,V c2 is the voltage value of the power supply VC2 of the analog-to-digital converter;

[0031] S2, adjust the overall current gain coefficient λ of the circuit, so that

[0032] Among them, V c2 is the voltage of the power supply VC2 of the analog-to-digital converter, ε is the margin left by the dynamic range of the input voltage of the analog-to-digital converter, and ε is the set value; i xM is the maximum value of the current amplitude to be measured.

[0033] Parameter v N Adjustment:

[0034] Connect a high-precision first DC voltmeter between the non-inverting input terminal of the first operational amplifier U3 and GND, connect a high-precision second DC voltmeter between the power supply VC2 of the analog-to-digital converter and GND, and adjust the second potentiometer R3 until the reading of the first DC voltmeter is equal to half of the reading of the second DC voltmeter, so that v N =V c2 / 2.

[0035] Tuning of parameter λ:

[0036] A power frequency sinusoidal AC constant voltage source v S Connect a load resistor R in series with V SM Indicates v S The amplitude of V SM and R, so that V SM / R xM ​, even if the constant voltage source v S The current generated by the load resistance R is within the current range i of the Hall current sensor. xM Then the constant voltage source v S The series branch with the load resistor R is then connected in series with the first high-precision true RMS AC ammeter. The two terminals of the series branch formed by these three devices are respectively connected to the two current input pins IP+ and IP- of the Hall current sensor. This method can apply a constant AC current i to be measured to the input pin of the Hall current sensor. x , from the first high-precision true RMS AC ammeter, i can be read x The effective value is I x Connect the second high-precision true RMS AC voltmeter to the output terminal and the non-inverting input terminal of the first operational amplifier U3. The AC voltage v between the output terminal and the non-inverting input terminal of the first operational amplifier U3 can be read by the second high-precision true RMS AC voltmeter. DS The effective value is V DS ;calculate By adjusting the resistance of the first potentiometer R2 in the circuit, V DS , so that V DS =λI x , that is, the calibration of λ is completed.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention is aimed at the specific field of measuring AC current containing harmonics in a detection circuit of AC current containing harmonics. The technical solution proposed in the present invention converts a low-performance, low-precision Hall current sensor with zero current output voltage that has no external output into an AC current measurement circuit with high precision, in which the bias voltage can be output externally, and the bias voltage and current gain coefficient can be independently adjusted, thereby effectively improving the measurement accuracy of the Hall current sensor.

[0039] 2. The design of the high-pass filter circuit, the reverse amplifier circuit and the DC bias circuit in the detection circuit of the harmonic AC current of the present invention makes the bias voltage and the gain coefficient adjustable, reduces the matching requirements for the power supply voltage of the Hall current sensor and the power supply voltage of the digital-to-analog converter, and thus makes the selection of components more flexible; at the same time, because the models of the Hall current sensor are not continuous, according to the maximum range of the measured current, the models of the Hall current sensor are generally divided into grades such as ±2.5A, ±5A, ±10A, ±20A, ±30A, etc., if the maximum value of the current to be measured does not completely match the maximum range of the current range of the Hall current sensor, the range of the analog-to-digital converter will not be fully utilized, resulting in a decrease in accuracy; the scheme proposed in the present invention can make the analog-to-digital converter input signal reach the maximum voltage dynamic range within the positive and negative power rails, so that the range of the analog-to-digital converter is fully utilized, which is beneficial to the improvement of the accuracy of the entire system.

[0040] 3. The parameter adjustment method of the detection circuit containing harmonic AC current of the present invention introduces the bias voltage v N The calibration method of the overall current gain coefficient λ is introduced to make full use of the range of the analog-to-digital converter and improve the measurement accuracy of the circuit; at the same time, the calibration method of the overall current gain coefficient λ is introduced to offset the errors of parameters such as R1, R2 and K through calibration, improve the measurement accuracy, and ensure the accurate measurement of the Hall current sensor.

[0041] 4. The present invention aims at the measurement requirements of AC current measurement containing harmonics, and changes v Q The Hall sensor without external output, high-pass filter, and operational amplifier circuit are organically integrated together to cleverly achieve a high-precision, v Q Can be output externally, v Q The AC current measurement circuit based on Hall sensor can adjust K and K independently. The whole circuit is simple, efficient and cost-effective. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a circuit schematic diagram of the present invention.

[0043] Figure 2 It is a schematic diagram of embodiment 1 of the present invention.

[0044] Figure 3 1 is a schematic diagram of an AC equivalent circuit of a high-pass filter composed of a first capacitor C1 and a resistor R1 in Example 1.

[0045] Figure 4 It is a schematic diagram of embodiment 3 of the present invention.

[0046] Figure 5 It is a schematic diagram of an existing current detection circuit composed of a Hall current sensor.

[0047] In the figure: Hall current sensor 1, high-pass filter circuit 2, reverse amplifier circuit 3, DC bias circuit 4, analog-to-digital converter 5. DETAILED DESCRIPTION

[0048] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0049] Embodiment 1:

[0050] See also Figures 2 to 3 , a detection circuit for harmonic AC current, comprising:

[0051] Hall current sensor 1, used to collect input current i x And converted into Hall potential signal v A Output;

[0052] The high-pass filter circuit 2 is connected in series to the signal output terminal Vout of the Hall current sensor 1, and is used to filter out the zero current bias voltage v in the Hall potential output by the Hall current sensor 1. Q , retain the AC voltage signal v AS , v A =v Q +v AS , AC voltage signal v AS After passing through the high-pass filter circuit 2, the attenuated AC voltage signal v is obtained. BS ;

[0053] The reverse amplifier circuit 3, whose inverting input terminal is connected in series with the filter circuit 2, is used to receive the attenuated AC voltage signal v at the inverting input terminal. BS Amplify and output the amplified voltage signal v D ;

[0054] The high-pass filter circuit 2 is an RC filter circuit formed by connecting a first capacitor C1 and a resistor R1 in series. The AC minimum attenuation rate β of the high-pass filter circuit 2 min =0.9999, then we can approximately assume that v BS＝ v AS ;

[0055] The reverse amplifier circuit 3 is obtained by connecting a first potentiometer R2 in parallel between the inverting input terminal and the signal output terminal of the first operational amplifier U3, and connecting a resistor R1 to the inverting input terminal of the first operational amplifier U3;

[0056] The high-pass filter circuit 2 and the reverse amplifier circuit 3 share a resistor R1;

[0057] The current value to be measured is

[0058] Where Vc2 is the voltage value of the power supply VC2 of the analog-to-digital converter 5, n is the number of bits of the conversion result of the analog-to-digital converter 5, λ is the overall current gain coefficient of the circuit, K is the current gain coefficient of the Hall current sensor 1.

[0059] The resistor R1 and the first capacitor C1 satisfy the following relationship:

[0060]

[0061] In the above formula, β min is the minimum amplitude attenuation rate allowed by the high-pass filter circuit 2 composed of the resistor R1 and the first capacitor C1, θ max is the maximum phase difference allowed by the output signal of the high-pass filter circuit 2 relative to the input signal, ω min is the AC current i to be detected x The lowest angular frequency.

[0062] The DC bias circuit 4 is connected to the in-phase input terminal of the reverse amplifier circuit 3 and is used to amplify the AC voltage signal v D Provides an adjustable DC bias voltage signal v N ;

[0063] The DC bias circuit 4 includes a second potentiometer R3 and a second capacitor C2, wherein two fixed terminals of the second potentiometer R3 are respectively connected to the power supply VC2 and the ground; a sliding terminal of the second potentiometer R3 is simultaneously connected to the in-phase input terminal of the reverse amplifier circuit 3 and the second signal input terminal IN2 of the analog-to-digital converter 5; and the in-phase input terminal of the reverse amplifier circuit 3 is connected in series with the second capacitor C2 and then to the ground.

[0064] The analog-to-digital converter 5 has a first signal input terminal IN1 connected to the signal output terminal of the reverse amplifier circuit 3, and a second signal input terminal IN2 connected to the in-phase input terminal of the reverse amplifier circuit 3, and is used to convert the received amplified voltage signal v D With the DC bias voltage signal v N Converted into digital signal Data_v D and Data_v N , and then compare the two signals to calculate the current value i to be measured x Output.

[0065] There are many types of Hall current sensors. The Hall current sensor mentioned in the technical solution of the present invention refers to an open-loop Hall current sensor, and its v Q There is no external output. For this type of open-loop Hall current sensor, it is referred to as Hall current sensor in the present invention. QA Hall current sensor without external output means that except for the output voltage signal pin Vout, there is no other dedicated pin to output V Q Signal.

[0066] Use i x It represents the instantaneous value of the current to be measured, which is an industrial frequency AC current containing harmonics and does not contain a DC component.

[0067] Working principle:

[0068] Current to be measured i x from Figure 2 The Hall current sensor U1 in the pin IP+ flows into the A Represents the voltage of the output pin Vout of the Hall current sensor U1, v A The reference point is the voltage GND of the ground pin of the Hall current sensor. According to the properties of the Hall current sensor, we can get formula (2):

[0069] v A =v Q +K·i x (2)

[0070] In formula (2), i x The unit is ampere, i x is a signed quantity, when i x The actual direction is to flow into the positive pin of the Hall current sensor input current, that is, the IP+ pin. x The actual direction is to flow out of the positive pin of the Hall current sensor input current, that is, the IP+ pin is negative; v Q is the zero current output voltage of the Hall current sensor, that is, the output voltage v when the input current i is 0 A The value of v Q The unit of is volt; K is the current gain coefficient of the Hall current sensor, and the unit of K is ohm. Ideally, K is a constant.

[0071] Use v AS Indicates v A The AC component of

[0072] v AS =K·i x (3)

[0073] Then formula (2) can be transformed into:

[0074] v A =v Q +v AS (4)

[0075] In formula (4), v Qis the DC component, v AS For the exchange quantity.

[0076] According to the principle of "virtual short" of op amp, Figure 2 The potentials of the in-phase terminal N and the reverse terminal M of the first operational amplifier U3 are equal, Figure 2 The first capacitor C1 and resistor R1 in the figure form a high-pass filter, and its AC equivalent circuit is as follows: Figure 3 As shown, use v BS express Figure 2 The voltage of point B to the AC ground N in the figure can be obtained by using the phasor analysis method:

[0077]

[0078] In formula (5), v AS The phasor corresponding to the sinusoidal signal with intermediate frequency ω is: v BS The phasor corresponding to the sinusoidal signal with an intermediate frequency of ω, ω is the angular frequency of the sinusoidal AC signal.

[0079] From formula (5), the amplitude-frequency characteristic and phase-frequency characteristic can be obtained as follows:

[0080]

[0081] In the above formula, β represents the attenuation rate of the AC signal amplitude, and θ represents and Assuming the minimum allowable attenuation rate is β min , the maximum phase difference is θ max , the lowest angular frequency of the detected AC current is ω min , the lowest frequency is f min , there is min =2πf min , then it can be deduced from equations (6) and (7) that the resistance R1 of the resistor R1 and the capacitance C1 of the first capacitor C1 should simultaneously satisfy the following relationship:

[0082]

[0083] If we take β min =0.9999,θ max =0.75°, f min =5Hz, then it can be deduced from equations (8) and (9) that: R1C1≥2.43s, and only C1=10μF, R1=250kΩ can meet the requirement. Under this parameter condition, because the attenuation rate is extremely small, it can be approximately considered that v AS With v BS Equal, that is:

[0084] vBS＝ v AS (10)

[0085] According to the principle of "virtual short" and "virtual open" of operational amplifier and the basic analysis method of circuit, the following formula can be derived:

[0086]

[0087] In formula (11), v DS is the voltage of the output terminal D of the first operational amplifier U3 to the AC ground.

[0088] Combining equations (11), (10) and (3), we can obtain:

[0089]

[0090] make:

[0091]

[0092] In the above formula, λ can be regarded as the current gain coefficient of the entire circuit.

[0093] Then, formula (12) can be changed into:

[0094] v DS =λi x (14)

[0095] From formula (14), we can see that v DS and i x There is a linear relationship, so the errors of parameters such as R1, R2 and K can be offset through calibration to improve the measurement accuracy.

[0096] Use v D represents the voltage of the output terminal D of the first operational amplifier U3 to GND, then:

[0097] v D =v N +v DS =v N +λi x (15)

[0098] In formula (15), v N is the voltage of the AC ground N to GND. It can be seen that the output characteristic of the Hall current sensor (15) and (2) are the same in form; the difference is that the two parameters v in (15) are N Both λ and v can be adjusted flexibly. N can be measured; and the two parameters v of formula (2) Q and K are not adjustable, and v Q Not exported and cannot be measured.

[0099] like Figure 2 As shown, the analog-to-digital converter input channel IN1 can measure v D The digital value Data_v D , the analog-to-digital converter input channel IN2 can measure v N The digital value Data_v N , these two digital quantities need to be measured simultaneously or in sequence with a short interval. Assuming the number of bits of the analog-to-digital converter is n, then, v DS It can be expressed as:

[0100]

[0101] Find v DS Then, according to formula (14), we can calculate i x :

[0102]

[0103] According to formula (17), we can measure i x .

[0104] Assume that the analog-to-digital converter is powered by a single power supply, and the voltage of its power supply VC2 is V c2 To make the input voltage of the analog-to-digital converter reach the maximum dynamic range, that is, to make full use of the range of the analog-to-digital converter, it is necessary to make the parameter v N and λ are taken as follows:

[0105] v N =V c2 / 2 (18)

[0106]

[0107] In formula (19), ε is the margin left by the dynamic range of the input voltage of the analog-to-digital converter. ε can be 0 or a smaller voltage value, which is selected according to the specific circuit conditions; i xM is the maximum value of the current amplitude to be measured.

[0108] The parameter v in the circuit is adjusted as follows N and λ, the parameter v N and λ are accurately adjusted to the values ​​set by equations (18) and (19):

[0109] The parameter λ is adjusted according to the v reflected by formula (14): DS 、i xThe relationship between and λ is used to adjust λ, but formula (14) is the relationship of AC instantaneous value, and AC instantaneous value changes at all times and is difficult to measure at the same time. The present invention cleverly uses sinusoidal AC signal as the debugging signal and uses effective value instead of instantaneous value for adjustment, because for two sinusoidal AC signals, if their instantaneous values ​​satisfy the proportional relationship, then their effective values ​​also satisfy the same proportional relationship. By adjusting the resistance R2 of the first potentiometer R2 in the circuit, V DS =λI x , that is, the calibration of λ is completed.

[0110] Through the above adjustment, the parameter v N and λ are not affected by the parameter errors of the components in the circuit, and the parameter v N The accuracy of and λ is only related to the accuracy level of the instrument used for calibration. Therefore, the parameter v N and λ can achieve very high accuracy.

[0111] A method for adjusting parameters of a detection circuit containing harmonic alternating current comprises the following steps:

[0112] S1, adjust the DC bias voltage signal v N , so that v N =V c2 / 2,V c2 is the voltage value of the power supply VC2 of the analog-to-digital converter 5;

[0113] S2, adjust the overall current gain coefficient λ of the circuit, so that

[0114] Wherein, Vc2 is the voltage of the power supply VC2 of the analog-to-digital converter 5, ε is the margin left for the dynamic range of the input voltage of the analog-to-digital converter 5, and ε is the set value; i xM is the maximum value of the current amplitude to be measured.

[0115] Parameter v N Adjustment:

[0116] Connect a high-precision first DC voltmeter between the non-inverting input terminal of the first operational amplifier U3 and GND, connect a high-precision second DC voltmeter between the power supply VC2 of the analog-to-digital converter and GND, and adjust the second potentiometer R3 until the reading of the first DC voltmeter is equal to half of the reading of the second DC voltmeter, so that v N =V c2 / 2.

[0117] Tuning of parameter λ:

[0118] A power frequency sinusoidal AC constant voltage source v S Connect a load resistor R in series with V SMIndicates v S The amplitude of V SM and R, so that V SM / R xM , even if the constant voltage source v S The current generated by the load resistance R is within the current range i of the Hall current sensor. xM Then the constant voltage source v S The series branch with the load resistor R is then connected in series with the first high-precision true RMS AC ammeter. The two terminals of the series branch formed by these three devices are respectively connected to the two current input pins IP+ and IP- of the Hall current sensor. This method can apply a constant AC current i to be measured to the input pin of the Hall current sensor. x , from the first high-precision true RMS AC ammeter, i can be read x The effective value is I x Connect the second high-precision true RMS AC voltmeter to the output terminal and the non-inverting input terminal of the first operational amplifier U3. The AC voltage v between the output terminal and the non-inverting input terminal of the first operational amplifier U3 can be read by the second high-precision true RMS AC voltmeter. DS The effective value is V DS ;calculate By adjusting the resistance of the first potentiometer R2 in the circuit, V DS , so that V DS =λI x , that is, the calibration of λ is completed.

[0119] Embodiment 2:

[0120] Embodiment 2 is substantially the same as Embodiment 1, except that:

[0121] See also Figure 1 The DC bias circuit 4 includes a second potentiometer R3 and a second operational amplifier U4, wherein the two fixed terminals of the second potentiometer R3 are respectively connected to the power supply VC2 and the ground; the sliding terminal of the second potentiometer R3 is connected to the in-phase input terminal of the second operational amplifier U4, the inverting input terminal of the second operational amplifier U4 is connected to the signal output terminal of the second operational amplifier U4, and the signal output terminal of the second operational amplifier U4 is simultaneously connected to the in-phase input terminal of the reverse amplifier circuit 3 and the second signal input terminal IN2 of the analog-to-digital converter 5.

[0122] The second operational amplifier U4 can stabilize the voltage at the in-phase input terminal of the reverse amplifier circuit 3 and the second signal input terminal IN2 of the analog-to-digital converter 5, thereby improving the measurement stability of the circuit.

[0123] Embodiment 3:

[0124] ​Embodiment 3 is substantially the same as Embodiment 2, except that:

[0125] See also Figure 4 The signal output terminal Vout of the Hall current sensor 1 is connected in series with a third capacitor C3 and then grounded.

[0126] The Hall current sensor U1 uses ACS712ELCTR-05B-T from Jieshengwei, with a range of ±5A. The current gain coefficient of the Hall current sensor is K = 0.185V / A, and the supply voltage is V c1 =5V. According to the specification of the Hall current sensor, a third capacitor C3 for noise removal is added to the circuit, and its value is 1nF. Figure 4 The operational amplifiers U3 and U4 in the system are dual operational amplifiers, model LMV722 from Youtai Company. Figure 4 The analog-to-digital converter U2 in the microcontroller STM32G030K6 uses the analog-to-digital converter built into the microcontroller. Its power supply voltage V c2 =3 V. The second capacitor C2 is 0.1 μF.

[0127] The maximum value of the measured AC current amplitude i xM =3A, the lowest frequency is 5Hz, take β min =0.9999,θ max =0.75°, f min =5Hz, then it can be concluded from equations (8) and (9) that: R1C1≥2.43s, and the requirement can be met by simply taking C1=10μF and R1=250kΩ.

[0128] From formula (18), we can calculate v N =1.5V.

[0129] ε is taken as 0.05V, and λ=0.48V / A can be calculated from formula (19).

[0130] From formula (13), it can be estimated that the theoretical resistance of potentiometer R2 should be R2 = -(λR1) / K = 649kΩ, so the potentiometer R2 is 1MΩ; if R2 only uses one potentiometer, its minimum adjustable resistance is too large, that is, the adjustment accuracy is insufficient. A fixed resistor can also be used in series with a potentiometer to replace the potentiometer R2.

[0131] The parameter v in the circuit is adjusted as follows N and λ, the parameter v N and λ are accurately adjusted to the values ​​set by equations (18) and (19):

[0132] Connect a high-precision DC voltmeter 1 between the in-phase terminal of the second operational amplifier U4 and GND, and also connect a high-precision DC voltmeter 2 between the power supply VC2 of the analog-to-digital converter and GND. Adjust the second potentiometer R3 until the reading of the DC voltmeter 1 is equal to half of the reading of the DC voltmeter 2, so that v N =V c2 / 2=1.5V.

[0133] A power frequency sinusoidal AC constant voltage source v S Connect a load resistor R in series with V SM Indicates v S The amplitude of V SM and R, so that V SM / R xM , even if the constant voltage source v S The current generated by the load resistor R is within the current range of the Hall current sensor, and then the constant voltage source v S The series branch with the load resistor R is then connected in series with a high-precision true RMS AC ammeter 3. The two terminals of the series branch composed of these three devices are connected to the two current input pins IP+ and IP- of the Hall current sensor respectively. This method can apply a constant AC current i to be measured to the input pin of the Hall current sensor. x , i can be read from the AC ammeter 3 x The effective value is I x ; Connect another high-precision true RMS AC voltmeter 4 to the output terminal D of the second operational amplifier U4 and the AC ground N. The AC voltage v between the output terminal D of the second operational amplifier U4 and the AC ground N can be read through the AC voltmeter 4. DS The effective value is V DS ; Using formula (19) to calculate λ = 0.48V / A, by adjusting the resistance value R2 of the first potentiometer R2 in the circuit, V DS =λI x =0.48I x , that is, the calibration of λ is completed.

[0134] like Figure 4 As shown, the analog-to-digital converter input channel IN1 can measure v D The digital value Data_v D , the analog-to-digital converter input channel IN2 can measure v N The digital value Data_v N , assuming the number of bits of the analog-to-digital converter is n, then, according to formula (17), we can measure i x .​

Claims

1. A detection circuit for harmonic alternating current, characterized in that: include: Hall current sensor (1), used to collect input current i x And converted into Hall potential signal v A Output; The high-pass filter circuit (2) is connected in series to the signal output terminal Vout of the Hall current sensor (1) and is used to filter out the zero current bias voltage v in the Hall potential output by the Hall current sensor (1). Q , retain the AC voltage signal v AS , v A =v Q +v AS , AC voltage signal v AS After passing through the high-pass filter circuit (2), the attenuated AC voltage signal v is obtained. BS ; The reverse amplifier circuit (3) has an inverting input terminal connected in series with the filter circuit (2) and is used to receive the attenuated AC voltage signal v at the inverting input terminal. BS Amplify and output the amplified voltage signal v D ; A DC bias circuit (4) is connected to the in-phase input terminal of the reverse amplifier circuit (3) and is used to bias the AC voltage signal v amplified by the reverse amplifier circuit (3) D Provides an adjustable DC bias voltage signal v N ; The analog-to-digital converter (5) has a first signal input terminal IN1 connected to the signal output terminal of the reverse amplifier circuit (3), and a second signal input terminal IN2 connected to the in-phase input terminal of the reverse amplifier circuit (3), and is used to receive the amplified voltage signal v D With the DC bias voltage signal v N Converted into digital signal Data_v D and Data_v N , and then compare the two signals to calculate the current value i to be measured x Output.

2. A detection circuit for harmonic AC current according to claim 1, characterized in that: The high-pass filter circuit (2) is an RC filter circuit formed by connecting a first capacitor C1 and a resistor R1 in series. The AC minimum attenuation rate β of the high-pass filter circuit (2) is min =0.9999, then we can approximately assume that v BS＝ v AS ; The reverse amplifier circuit (3) is obtained by connecting a first potentiometer R2 in parallel between the inverting input terminal and the signal output terminal of the first operational amplifier U3, and connecting the inverting input terminal of the first operational amplifier U3 to a resistor R1; The high-pass filter circuit (2) and the reverse amplifier circuit (3) share a resistor R1; The current value to be measured is Where V c2 is the voltage value of the power supply VC2 of the analog-to-digital converter (5), n is the number of bits of the conversion result of the analog-to-digital converter (5), λ is the overall current gain coefficient of the circuit, K is the current gain coefficient of the Hall current sensor (1).

3. A detection circuit for harmonic AC current according to claim 2, characterized in that: The resistor R1 and the first capacitor C1 satisfy the following relationship: In the above formula, β min is the minimum amplitude attenuation rate allowed by the high-pass filter circuit (2) composed of the resistor R1 and the first capacitor C1, θ max is the maximum phase difference allowed between the output signal of the high-pass filter circuit (2) and the input signal, ω min is the AC current i to be detected x The lowest angular frequency.

4. A detection circuit for harmonic AC current according to claim 1, 2 or 3, characterized in that: The DC bias circuit (4) comprises a second potentiometer R3 and a second capacitor C2, wherein two fixed terminals of the second potentiometer R3 are respectively connected to a power supply VC2 and a ground; a sliding terminal of the second potentiometer R3 is simultaneously connected to a non-inverting input terminal of the reverse amplifier circuit (3) and a second signal input terminal IN2 of the analog-to-digital converter (5); The non-inverting input terminal of the reverse amplifier circuit (3) is connected in series with a second capacitor C2 and then grounded.

5. A detection circuit for harmonic AC current according to claim 1, 2 or 3, characterized in that: The DC bias circuit (4) comprises a second potentiometer R3 and a second operational amplifier U4, wherein two fixed terminals of the second potentiometer R3 are respectively connected to a power supply VC2 and a ground; a sliding terminal of the second potentiometer R3 is connected to a non-inverting input terminal of the second operational amplifier U4, an inverting input terminal of the second operational amplifier U4 is connected to a signal output terminal of the second operational amplifier U4, and the signal output terminal of the second operational amplifier U4 is simultaneously connected to a non-inverting input terminal of the reverse amplifier circuit (3) and a second signal input terminal IN2 of the analog-to-digital converter (5).

6. The detection circuit for harmonic AC current according to claim 5, characterized in that: The signal output terminal Vout of the Hall current sensor (1) is connected in series with a third capacitor C3 and then grounded.

7. A parameter adjustment method for a detection circuit containing harmonic alternating current based on any one of claims 1 to 7, characterized in that: The steps include: S1, adjust the DC bias voltage signal v N , so that v N =V c2 / 2,V c2 is the voltage value of the power supply VC2 of the analog-to-digital converter (5); S2, adjust the overall current gain coefficient λ of the circuit, so that Wherein, Vc2 is the voltage of the power supply VC2 of the analog-to-digital converter (5), ε is the margin left by the dynamic range of the input voltage of the analog-to-digital converter (5), and ε is the set value; i xM is the maximum value of the current amplitude to be measured.

8. The parameter adjustment method for a detection circuit containing harmonic alternating current according to claim 7, characterized in that: Parameter v N Adjustment: Connect a high-precision first DC voltmeter between the non-inverting input terminal of the first operational amplifier U3 and GND, connect a high-precision second DC voltmeter between the power supply VC2 of the analog-to-digital converter and GND, and adjust the second potentiometer R3 until the reading of the first DC voltmeter is equal to half of the reading of the second DC voltmeter, so that v N =V c2 / 2.

9. The parameter adjustment method for a detection circuit containing harmonic alternating current according to claim 7, characterized in that: Tuning of parameter λ: A power frequency sinusoidal AC constant voltage source v S Connect a load resistor R in series with V SM Indicates v S The amplitude of V SM and R, so that V SM / R xM , even if the constant voltage source v S The current generated by the load resistor R is within the current range i of the Hall sensor. xM Then the constant voltage source v S The series branch with the load resistor R is then connected in series with the first high-precision true RMS AC ammeter. The two terminals of the series branch formed by these three devices are respectively connected to the two current input pins IP+ and IP- of the Hall sensor. This method can apply a constant AC current i to be measured to the input pin of the Hall sensor. x , from the first high-precision true RMS AC ammeter, i can be read x The effective value is I x Connect the second high-precision true RMS AC voltmeter to the output terminal and the non-inverting input terminal of the first operational amplifier U3. The AC voltage v between the output terminal and the non-inverting input terminal of the first operational amplifier U3 can be read by the second high-precision true RMS AC voltmeter. DS The effective value is V DS ;calculate By adjusting the resistance of the first potentiometer R2 in the circuit, V DS , so that V DS =λI x , that is, the calibration of λ is completed.​

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