A Closed-Loop Control Method for Zero Flux DC Current Sensor

Abstract

This invention relates to the field of current sensor design and control technology, and more particularly to a zero-flux DC current sensor closed-loop control method based on fluxgate technology, independent of bandpass filters. The method mainly includes the following steps: S1, applying an AC excitation signal to the excitation winding in the DC current sensor's magnetic core probe via a sine wave or triangular wave generator circuit; S2, using the excitation source signal and the winding excitation current sampling signal as the source of the zero-flux closed-loop feedback control signal; S3, performing absolute value, pure delay, and simple addition and subtraction operations on the above control signal; S4, using the processed control signal as the input to a PI controller to generate a compensation winding voltage drive signal, thereby achieving accurate measurement of the measured current. This method, through optimized signal processing and closed-loop control strategies, achieves accurate measurement of DC current and significantly improves the system's dynamic response characteristics and measurement accuracy.

Description

Technical Field

[0001] This invention relates to the field of current sensor design and control technology, and more particularly to a closed-loop control method for a zero-flux DC current sensor based on fluxgate technology, which does not rely on bandpass filters. Background Technology

[0002] High-precision DC current measurement is typically achieved using fluxgate current sensors, which rely on zero-flux technology to ensure accuracy. Zero-flux technology ensures that the measured current cancels out the magnetic flux generated in the core by the compensating winding, keeping the magnetic flux in the core zero, thus achieving high-precision current measurement.

[0003] Fluxgate current sensors are widely used in various fields due to their high sensitivity, good linearity, high resolution, and high accuracy. These sensors are suitable not only for DC or low-frequency AC measurements but also for stable operation in high-temperature environments. To improve measurement accuracy, closed-loop control technology is often employed. The traditional closed-loop control system operates based on the nonlinear characteristics of ferromagnetic materials and an external excitation signal. The measured signal is modulated into an alternating magnetic field, and then demodulated to obtain a feedback control signal, thus forming a closed-loop control.

[0004] However, traditional fluxgate current sensors often employ the second harmonic method for signal processing, relying on high-order bandpass filters to extract the second harmonic excitation signal related to the measured current. When the excitation signal frequency is low, this not only complicates filter design but also causes significant signal attenuation and phase delay, affecting the system's dynamic response. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a closed-loop control method for a zero-flux DC current sensor that does not rely on a high-order bandpass filter. This method utilizes the excitation source signal and the winding excitation current sampling signal as the signal source for closed-loop feedback control. By performing absolute value calculations, pure delays, and simple addition and subtraction operations on these signals, followed by processing by a PI controller, the current of the compensation winding can be precisely controlled. Based on the turns ratio of the compensation winding to the measured current winding, the magnitude of the primary measured current can be accurately calculated.

[0006] The technical solution adopted in this invention is: a closed-loop control method for a zero-flux DC current sensor, which mainly includes the following steps:

[0007] S1. Apply an AC excitation signal to the excitation winding in the magnetic core probe of the DC current sensor through a sine wave or triangular wave generating circuit.

[0008] S2. Use the excitation source signal and the winding excitation current sampling signal as the source of the zero flux closed-loop feedback control signal;

[0009] S3. Perform absolute value, pure delay, and simple addition and subtraction operations on the above control signals;

[0010] S4. The processed control signal is used as the input of the PI controller to generate a compensation winding voltage drive signal, thereby realizing the accurate measurement of the measured current.

[0011] The control method is implemented in the following steps:

[0012] Step 1: Apply an AC voltage excitation signal u with a period of T to the input terminals of the two sets of excitation windings a and b in the magnetic core probe of the DC current sensor through a sine wave or triangular wave generating circuit. ex Simultaneously, the voltage excitation signal u ex Find the absolute value, and then convert the signal u after finding the absolute value. ex Let it be u exabs ;

[0013] Step 2: Obtain the sampling voltage u through the sampling resistors Ra and Rb at the output terminals of the two sets of excitation windings a and b, respectively. ea and u eb Then, the sampling voltage difference signal u between sampling resistors Ra and Rb is obtained. eab =u ea -u eb ;

[0014] Step 3: Transfer signal u exabs and the sampled voltage difference signal u eab The data is fed into two delay circuits, each with a delay time of T / 4. Let the output of each delay circuit be u. exabs_d and u eab_d The difference between the two signals will be used to obtain the signal u. exabs1 , will u eab with u eab_d Difference to obtain u eab1 , that is u exabs1 =u exabs -u exabs_d u eab1 =u eab -u eab_d ;

[0015] Step 4: Apply the following rules to signal u exabs1 and u eab1 After synchronous demodulation, u is obtained eab2 :

[0016] If u exabs1 ≥0, then u eab2 =u eab1 ;

[0017] If u exabs1 <0, then ueab2 =0;

[0018] Step 5: Apply the u obtained in Step 4 eab2 Perform the integration operation and denote the result as u. eab3 , that is u eab3 =∫u eab2 dt;

[0019] Step 6: Take the u obtained in Step 5 eab3 As the input to the PI controller, the output of the PI controller is the voltage drive signal of the flux compensation winding of the zero flux current DC current sensor. The product of the compensation winding current and the turns ratio is the primary measured current.

[0020] The voltage excitation signal u ex When it is a sine wave, the expression is:

[0021] u ex =U ex sin(ωt)

[0022] U ex The amplitude of the sine wave signal. The electric angular velocity of the sinusoidal signal is given by t, where t is time and the excitation signal is u. ex When it is a triangular wave, the expression is:

[0023]

[0024] U max The amplitude of the triangular wave signal. Let t be the electrical angular velocity of the triangular wave signal, t be time, and n be the nth excitation signal period.

[0025] The two sets of excitation windings a and b are respectively wound on two sets of soft magnetic cores with the same characteristics. The two sets of excitation windings a and b have the same number of turns, but the winding directions are opposite, so that the excitation current caused by the excitation voltage in the two sets of excitation windings a and b is in opposite directions.

[0026] The sampling resistors Ra and Rb at the output terminals of the two sets of excitation windings a and b have the same resistance value.

[0027] The turns ratio in step 6 refers to the ratio of the number of turns in the compensation winding coil to the number of turns in the primary measured current coil.

[0028] The delay circuit in step 3 is used to ensure the synchronization of signal processing.

[0029] The synchronous demodulation process in step 4 is used to extract signals related to the measured current.

[0030] The output signal of the PI controller is used to drive the compensation winding to generate a compensation current in the opposite direction to the measured current, thereby achieving a zero flux state.

[0031] The method is applicable to the measurement of direct current, and the measurement accuracy is improved through closed-loop control.

[0032] The technical effects achieved by this invention are as follows: This technical solution addresses the problems of reliance on high-order bandpass filters and the resulting complex structural parameter design, signal attenuation, and phase delay in traditional fluxgate DC current sensor closed-loop control methods. It proposes a zero-flux DC current sensor closed-loop control method based on fluxgate technology and independent of bandpass filters. This method achieves accurate DC current measurement and significantly improves the system's dynamic response characteristics and measurement accuracy by optimizing signal processing and closed-loop control strategies. Specifically, this is manifested in the following ways: First, simplified circuit structure and design: This technical solution avoids the use of high-order bandpass filters, instead employing pure delay circuits and simple mathematical operations for signal processing, thus significantly simplifying the circuit structure and design and reducing manufacturing costs and complexity. Second, optimized dynamic response characteristics: By reducing the signal attenuation and phase delay problems caused by high-order bandpass filters, this technical solution improves the system's dynamic response characteristics, enabling the sensor to achieve more accurate and precise measurements in real-world applications. In current measurement, it can respond to current changes more quickly and accurately; secondly, it improves measurement accuracy: through precise processing of the excitation source signal and the winding excitation current sampling signal, combined with the fine control of the PI controller, this technical solution achieves precise control of the compensation winding current, thereby improving the measurement accuracy of the primary measured current; finally, it expands the applicability: the zero flux DC current sensor based on fluxgate technology itself has the advantages of high sensitivity, good linearity, high resolution and high accuracy. This technical solution further enhances its application adaptability in complex environments such as high temperature and strong magnetic field by optimizing the closed-loop control method. Attached Figure Description

[0033] Figure 1 This is a block diagram of a DC current sensor based on fluxgate closed-loop control technology.

[0034] Figure 2 This is a control block diagram for a DC current sensor based on the second harmonic method using a high-order bandpass filter.

[0035] Figure 3 This is a closed-loop control block diagram of the zero-flux DC current sensor proposed in this invention;

[0036] Figure 4 This is a block diagram of the delay circuit and the signal difference processing;

[0037] Figure 5 It is the waveform of the actual measured current in the primary winding and the measured current calculated by the compensated winding. Detailed Implementation

[0038] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings:

[0039] Combination Figure 1-5 As shown, a closed-loop control method for a zero-flux DC current sensor that does not rely on a high-order bandpass filter is implemented as follows:

[0040] Step 1: Apply an AC current with a period of T = 0.02s and an amplitude of U to the input terminals of two sets of excitation windings a and b in the DC current sensor core probe, which have the same number of turns but opposite winding directions. max =28V triangular wave excitation voltage signal u ex and u ex u is obtained through an absolute value circuit. exabs , then u ex and u exabs The mathematical expression can be represented as

[0041]

[0042] Step 2: Obtain the sampling resistors Ra and Rb voltage u at the output terminals of the two sets of excitation windings a and b. ea and u eb And further obtain the voltage difference signal u between the two. eab =u ea -u eb ;

[0043] Step 3: Transfer signal u exabs and the sampled voltage difference signal u eab The data is fed into two delay circuits, each with a delay time of T / 4 = 0.005s. Let the output of each delay circuit be u. exabs_d and u eab_d , will u exabs with u exabs_d The signal u is obtained by subtraction. exabs1 , will u eab with u eab_d Difference to obtain u eab1 , that is u exabs1 =u exabs -u exabs_d u eab1 =u eab -u eab_d The block diagram of the delay circuit and the signal difference processing in this step is as follows: Figure 4 As shown;

[0044] Step 4: Apply the following rules to signal u exabs1 and u eab1 After synchronous demodulation, u is obtainedeab2 :

[0045] If u exabs1 ≥0, then u eab2 =u eab1 ;

[0046] If u exabs1 <0, then u eab2 =0;

[0047] Step 5: Apply the u obtained in Step 4 eab2 Perform the integration operation and denote the result as u. eab3 , that is u eab3 =∫u eab2 dt;

[0048] Step 6: Take the u obtained in Step 5 eab3 As the input to the PI controller, the output of the PI controller is the voltage drive signal for the flux compensation winding of the zero flux current DC current sensor. The product of the compensation winding current and the turns ratio is the primary measured current. In this embodiment, the primary measured DC current is 12.5A, and the turns ratio is 400:1. The simulated waveforms of the actual primary measured current and the measured current calculated by the compensation winding are as follows: Figure 5 As shown.

[0049] Example 1: Implementation of a zero-flux DC current sensor based on fluxgate closed-loop control technology

[0050] This invention provides an embodiment of a zero-flux DC current sensor based on fluxgate closed-loop control technology. First, an AC triangular wave excitation voltage signal is input to the excitation windings a and b in the DC current sensor's core probe to ensure that the two windings have the same number of turns but opposite winding directions. Next, the absolute values ​​of the excitation voltage signals are obtained through an absolute value circuit and recorded as Va and Vb.

[0051] Subsequently, the voltage values ​​at the sampling resistors Ra and Rb at the output terminals of the two sets of excitation windings a and b are measured and denoted as Ura and Urb, respectively, and the voltage difference signal between them is calculated. To obtain more accurate measurement results, the voltage signal and the voltage difference signal are respectively fed into two delay circuits with the same delay time Δt. The output signals of the delay circuits are subtracted to obtain new signals ΔUa and ΔUb.

[0052] According to specific demodulation rules, signals ΔUa and ΔUb are synchronously demodulated, and then the demodulation results are integrated to obtain the integral result I_int. This integral result serves as the input to the PI controller, and its output is the drive signal for the flux compensation winding voltage of the zero flux current DC current sensor. This drive signal controls the current of the compensation winding so that its turns ratio product with the measured current equals the primary measured current, thus achieving zero flux measurement.

[0053] Example 2: Optimized Implementation of Zero Flux DC Current Sensor Combined with High-Order Bandpass Filter

[0054] Building upon Example 1, this example introduces a high-order bandpass filter to further optimize the performance of the zero-flux DC current sensor. The high-order bandpass filter effectively filters out noise interference during the measurement process, improving measurement accuracy.

[0055] First, by following the steps described in Example 1—inputting the excitation voltage signal, measuring the voltage of the sampling resistor, and processing with the delay circuit—the unmodulated signals ΔUa and ΔUb are obtained. Next, these two signals are fed into a high-order bandpass filter to further filter out high-frequency noise and low-frequency interference.

[0056] The filtered signal is then synchronously demodulated and integrated again to obtain the integral result I_int. Similar to Example 1, the integral result is used as the input of the PI controller to generate the flux compensation winding voltage drive signal for the zero flux current DC current sensor.

[0057] By incorporating a high-order bandpass filter, this embodiment can further improve the anti-interference capability and measurement accuracy of the DC current sensor while maintaining the high-precision measurement of fluxgate closed-loop control technology, making it suitable for application scenarios with higher measurement accuracy requirements.

[0058] In summary, in the technical solution of this invention, the extraction of the second harmonic signal only uses a pure delay circuit and simple addition and subtraction mathematical operations. Compared with the traditional method for extracting second harmonic signals from fluxgate current sensors based on high-order bandpass filters, this invention effectively avoids the problems of complex structural parameter design, signal attenuation, and dynamic response caused by phase delay due to high-order bandpass filters. Secondly, in this application, the synchronous demodulated signal is obtained by absolute value processing of the excitation source signal, followed by processing with a pure delay circuit and simple addition and subtraction mathematical operations. Compared with the traditional method for extracting second harmonic synchronous demodulated signals from fluxgate current sensors based on bandpass filters, parameter adjustment is simpler and can effectively improve dynamic response characteristics. Thirdly, compared with the traditional fluxgate current sensor based on analog circuits, this invention mainly uses a pure delay circuit and simple addition and subtraction mathematical operations to extract and process the signal. The storage units used are inherent in the digital controller itself, which is more conducive to the digital implementation of the fluxgate current sensor.

Claims

1. A closed-loop control method for a zero-flux DC current sensor, characterized in that: This method mainly includes the following steps: S1. Apply an AC excitation signal to the excitation winding in the magnetic core probe of the DC current sensor through a sine wave or triangular wave generating circuit. S2. Use the excitation source signal and the winding excitation current sampling signal as the source of the zero flux closed-loop feedback control signal; S3. Perform absolute value, pure delay, and simple addition and subtraction operations on the above control signals; S4. The processed control signal is used as the input of the PI controller to generate a compensation winding voltage drive signal, thereby realizing the accurate measurement of the measured current. The control method is implemented in the following steps: Step 1: Apply an AC voltage excitation signal u with a period of T to the input terminals of the two sets of excitation windings a and b in the magnetic core probe of the DC current sensor through a sine wave or triangular wave generating circuit. ex Simultaneously, the voltage excitation signal u ex Find the absolute value, and then convert the signal u after finding the absolute value. ex Let it be u exabs ; Step 2: Obtain the sampling voltage u through the sampling resistors Ra and Rb at the output terminals of the two sets of excitation windings a and b, respectively. ea and u eb Then, the sampling voltage difference signal u between sampling resistors Ra and Rb is obtained. eab =u ea -u eb ; Step 3: Transfer signal u exabs and the sampled voltage difference signal u eab The data is fed into two delay circuits, each with a delay time of T / 4. Let the output of each delay circuit be u. exabs_d and u eab_d , will signal u exabs with u exabs_d The signal u is obtained by subtraction. exabs1 , will u eab with u eab_d Difference to obtain u eab1 , that is u exabs1 =u exabs -u exabs_d u eab1 =u eab -u eab_d ; Step 4: Apply the following rules to signal u exabs1 and u eab1 After synchronous demodulation, u is obtained eab2 : If u exabs1 ≥0, then u eab2 =u eab1 ; If u exabs1 <0, then u eab2 =0; Step 5: Apply the u obtained in Step 4 eab2 Perform the integration operation and denote the result as u. eab3 , that is u eab3 =∫u eab2 dt; Step 6: Take the u obtained in Step 5 eab3 As the input to the PI controller, the output of the PI controller is the voltage drive signal of the flux compensation winding of the zero flux current DC current sensor. The product of the compensation winding current and the turns ratio is the primary measured current.

2. The closed-loop control method for a zero-flux DC current sensor according to claim 1, characterized in that: Voltage excitation signal u ex When it is a sine wave, the expression is: u ex =U ex sin(ωt) U ex The amplitude of the sine wave signal. The electric angular velocity of the sinusoidal signal is given by t, where t is time and the excitation signal is u. ex When it is a triangular wave, the expression is: U max The amplitude of the triangular wave signal. Let t be the electrical angular velocity of the triangular wave signal, t be time, and n be the nth excitation signal period.

3. The closed-loop control method for a zero-flux DC current sensor according to claim 1, characterized in that: Two sets of excitation windings a and b are wound on two sets of soft magnetic cores with the same characteristics. The two sets of excitation windings a and b have the same number of turns, but the winding directions are opposite, so that the excitation currents caused by the excitation voltage in the two sets of excitation windings a and b are in opposite directions.

4. The closed-loop control method for a zero-flux DC current sensor according to claim 1, characterized in that: The sampling resistors Ra and Rb at the output terminals of the two sets of excitation windings a and b have the same resistance value.

5. The closed-loop control method for a zero-flux DC current sensor according to claim 1, characterized in that: The turns ratio in step 6 refers to the ratio of the number of turns in the compensation winding coil to the number of turns in the primary current-measuring coil.

6. The closed-loop control method for a zero-flux DC current sensor according to claim 1, characterized in that: The delay circuit in step 3 is used to ensure the synchronization of signal processing.

7. The closed-loop control method for a zero-flux DC current sensor according to claim 1, characterized in that: The synchronous demodulation process in step 4 is used to extract signals related to the measured current.

8. The closed-loop control method for a zero-flux DC current sensor according to claim 1, characterized in that: The output signal of the PI controller is used to drive the compensation winding to generate a compensation current in the opposite direction to the measured current, thereby achieving a zero flux state.

9. A closed-loop control method for a zero-flux DC current sensor according to any one of claims 1-8, characterized in that: The method is applicable to the measurement of direct current, and the measurement accuracy is improved through closed-loop control.

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