A zero-flux digital DC current sensor closed-loop control method

Abstract

The application relates to a current sensor design and control technology, in particular to a closed-loop control method of a zero-flux digital direct-current sensor based on a fluxgate technology; the method comprises the following steps: sending on and off driving signals to two groups of switch tubes respectively, and simultaneously starting timers; switching the on state of the switch tubes according to the flip of the output level of a voltage comparator, and recording the timer time; calculating the time difference of the two timers, and taking the time difference as a feedback signal and sending the feedback signal into a digital PI controller; taking the output of the digital PI controller as a voltage driving signal of a compensation winding coil, and taking the current and turn ratio product of the compensation winding coil as the current of a primary measured current coil; repeating the above steps to obtain the current value of the primary measured current coil in real time; the application not only simplifies the manufacturing of a magnetic core probe, improves the anti-interference capability, but also reduces the digital design cost and improves the system flexibility, and provides a new thought and solution for the design and application of a current sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of current sensor design and control, in particular to the field of current measurement, and specifically to a closed-loop control method of a zero-flux digital DC current sensor based on a fluxgate technology. BACKGROUND

[0002] In the field of current measurement, the measurement of alternating current usually relies on a transformer, whose working principle is based on the law of electromagnetic induction. However, for the measurement of direct current, since the direct current cannot induce an alternating magnetic field in the magnetic core, it cannot be directly realized by the principle of the transformer. In order to solve this problem, the fluxgate current sensor emerged as the times require, which uses the fluxgate principle to modulate the measured direct current, and then demodulates it by a secondary coil to generate a compensation current, thereby realizing the measurement of direct current.

[0003] The fluxgate current sensor has been widely used in many fields due to its high sensitivity, good linearity, high resolution and high precision. The traditional fluxgate current sensor uses closed-loop control technology to improve measurement accuracy, but its magnetic core probe is complex to manufacture, and most of the analog devices are used to realize signal acquisition and processing, which has weak anti-interference ability. At the same time, in the digital implementation, the traditional method needs to rely on high-precision AD sampling chips, which increases the system hardware cost and complexity. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the present application provides a closed-loop control method of a zero-flux digital DC current sensor based on a fluxgate technology, which simplifies the manufacturing of the magnetic core probe, improves the anti-interference ability, and avoids the dependence on AD sampling chips, thereby realizing high-precision and low-cost measurement of direct current.

[0005] The technical solution adopted by the present application is as follows: a closed-loop control method of a zero-flux digital DC current sensor, comprising the following steps:

[0006] S1, initializing the driving signal: sending the on and off driving signals to the two groups of switching tubes respectively, and starting the timer at the same time;

[0007] S2, first flip detection: switching the on state of the switching tube according to the flip of the voltage comparator output level, and recording the timer time;

[0008] S3, second flip detection: calculating the time difference of the two timers, and sending it as a feedback signal to the digital PI controller;

[0009] S4, calculating the feedback signal: the output of the digital PI controller is used as the voltage driving signal of the compensation winding coil, and the current of the compensation winding coil multiplied by the turns ratio reflects the current of the primary measured current coil;

[0010] S5, loop control: repeat the above S1-S4 steps, real-time acquisition of the primary measured current coil current value.

[0011] The primary measured current coil, the magnetic head excitation coil and the compensation winding coil are all wound on the same magnetic core, and the magnetic head excitation coil is a single excitation winding.

[0012] The on or off driving signals of the two groups of switching tubes are respectively sent by two pins of the CPU, and each group of switching tubes includes two switching elements.

[0013] The voltage comparator is used for comparing the voltage across the current limiting resistor with the set voltage domain value, and the voltage comparator can be an analog voltage comparator or a digital voltage comparator.

[0014] When the voltage across the current limiting resistor reaches the set voltage domain value, the magnetic core enters a saturated state, and at this time the voltage comparator output level flips.

[0015] The voltage comparator output level flip means that its output changes from a positive maximum value to a negative maximum value, or from a negative maximum value to a positive maximum value.

[0016] The product of the compensation winding current and the turn ratio is used to calculate the current of the primary measured current coil, wherein the turn ratio refers to the ratio of the number of turns of the compensation winding coil to the number of turns of the primary measured current coil.

[0017] The digital PI controller adjusts the voltage driving signal of the compensation winding coil according to the feedback signal to realize accurate measurement of the current of the primary measured current coil

[0018] The technical effects achieved by the application are: the zero-flux digital DC current sensor closed-loop control method simplifies the manufacturing of the magnetic core probe, improves the anti-interference ability, reduces the digital design cost and improves the system flexibility, provides a new idea and solution for the design and application of the current sensor, and has obvious advantages and beneficial effects compared with the traditional technology, which is embodied in the following aspects:

[0019] (I) Simplify the manufacturing of the magnetic core probe: the traditional magnetic flux gate DC current sensor needs two sets of excitation winding coils with highly matched parameters, which not only increases the manufacturing complexity, but also puts forward high requirements for the consistency of the coil parameters. And the application only needs one set of excitation winding, without the need for coil parameter matching, thereby greatly simplifying the manufacturing process of the magnetic core probe and reducing the production difficulty and cost.

[0020] (II) Improve anti-interference ability: traditional magnetic flux gate DC current sensor adopts analog circuit to process signal, which is easy to be affected by electromagnetic interference. The present application adopts digital signal processing method, realizes accurate control through digital controller and PI controller, significantly improves the anti-interference ability of the sensor, and ensures the accuracy and stability of the measurement results.

[0021] (III) Reduce the cost of digital design: in the process of digital design of DC current sensor, the traditional method usually relies on high-precision AD sampling chip to quantize analog signal. The present application ingeniously avoids this demand, calculates the compensation current by directly using the duty cycle difference of PWM signal, thereby simplifying the circuit structure, reducing the hardware cost and system complexity.

[0022] (IV) Improve system flexibility: the control method of the present application is realized based on digital platform, which is convenient for integration and compatibility with existing digital system, improves the flexibility and scalability of the system. At the same time, digital control is also convenient for realizing more complex algorithms and strategies to further improve the performance and function of the sensor. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the logic block diagram of the DC current sensor structure based on the magnetic flux gate closed-loop control technology in the present application;

[0024] Figure 2 is the logic block diagram of the zero-flux digital DC current sensor closed-loop control structure in the present application;

[0025] Figure 3 is the waveform of the primary actual measured current and the measured current waveform calculated by the compensation winding in the present application.

[0026] Figure 4 is the waveform of the driving signal QD14, QD23 and the voltage VR across the current limiting resistor Ra in the present application. DETAILED DESCRIPTION

[0027] The present application provides a zero-flux digital DC current sensor closed-loop control method, which aims to simplify the manufacturing of magnetic core probe, improve the anti-electromagnetic interference ability, and avoid the dependence on high-precision AD sampling chip; the present application will be described in detail below in combination with the drawings and examples.

[0028] Example 1: zero-flux digital DC current sensor closed-loop control method

[0029] The specific implementation steps of the zero-flux digital DC current sensor closed-loop control method are as follows:

[0030] S1, initialization of driving signal: send off driving signal to switch tube T2 and T3, i.e. QD23 is low level; send on driving signal to switch tube T1 and T4, i.e. QD14 is high level; at the same time, start the timer and record the current time as t0; current path: VCC→switch tube T1→head exciting coil W2→switch tube T4→current limiting resistor Ra→GND; send voltage VR between current limiting resistor Ra (in this embodiment, Ra=1Ω) and set voltage domain value VS (in this embodiment, VS=0.3V) to positive and negative input terminals of voltage comparator respectively.

[0031] S2, first flip detection: when the output level of voltage comparator flips (i.e. from positive maximum value to negative maximum value, or from negative maximum value to positive maximum value), capture the event by digital controller pin P1; send off driving signal to switch tube T1 and T4, i.e. QD14 is low level; send on driving signal to switch tube T2 and T3, i.e. QD23 is high level; record the current timer time as t1, and calculate TP=t1-t0; current path: VCC→switch tube T2→head exciting coil W2→switch tube T3→current limiting resistor Ra→GND; keep sending voltage VR between current limiting resistor Ra and set voltage domain value VS to positive and negative input terminals of voltage comparator respectively.

[0032] S3, second flip detection: when the output level of voltage comparator flips again, capture the event by digital controller pin P1; send off driving signal to switch tube T2 and T3, i.e. QD23 is low level; send on driving signal to switch tube T1 and T4, i.e. QD14 is high level; record the current timer time as t2, and calculate TN=t2-t1.

[0033] S4, calculation of feedback signal: calculate T=TP-TN, and send T as feedback signal to digital PI controller in CPU; the output of PI controller is used as voltage driving signal of zero magnetic flux DC current sensor magnetic flux compensation winding coil W3; after amplification by power amplification unit, the driving signal acts on compensation winding coil W3 to generate compensation current; the product of current of compensation winding coil W3 and turns ratio (ratio of turns of compensation winding coil W3 to turns of primary measured current coil W1) is the current of primary measured current coil W1.

[0034] S5, loop control: repeat the above steps S1-S4 to obtain the current value of primary measured current coil W1 in real time.

[0035] In the embodiment, the primary measured current coil W1, the head excitation coil W2 and the compensation winding coil W3 are wound on the same magnetic core. The on or off driving signal QD14 of the switch tubes T1 and T4 is sent by the same pin P2 of the CPU; the on or off driving signal QD23 of the switch tubes T2 and T3 is sent by the same pin P3 of the CPU. The voltage comparator can be an analog voltage comparator or a digital voltage comparator. When the voltage VR across the current limiting resistor Ra reaches the set voltage domain value VS, the head magnetic core enters the saturation state. The output level of the voltage comparator is reversed, specifically, its output changes from the positive maximum value to the negative maximum value, or from the negative maximum value to the positive maximum value. The product of the compensation winding current and the turns ratio, which refers to the ratio of the number of turns of the compensation winding coil W3 to the number of turns of the primary measured current coil W1, is used to calculate the current of the primary measured current coil W1.

[0036] The embodiment effectively simplifies the manufacturing complexity of the magnetic core probe, improves the anti-electromagnetic interference capability of the sensor, and avoids the use of high-precision AD sampling chips in digital implementation, thereby reducing the system hardware cost and complexity. In the embodiment, when the primary measured direct current is 75A and the turns ratio is 400:1, the actual primary measured current and the measured current simulation waveform calculated by the compensation winding are as shown in Figure 3 The waveforms of the driving signals QD14, QD23 and the voltage VR across the current limiting resistor Ra are as shown in Figure 4

[0037] Embodiment 2: A zero-flux digital direct current sensor closed-loop control method based on the magnetic flux gate technology is provided.

[0038] The present application is further described below in combination with specific embodiment 2. The zero-flux digital direct current sensor closed-loop control method of the embodiment has the following specific steps:

[0039] S1, initialize the driving signal and the current path setting: send the off driving signal to the switch tubes T2 and T3, i.e. QD23 is low; send the on driving signal to the switch tubes T1 and T4, i.e. QD14 is high; at the same time, start the timer and record the current time as t0; the current path setting is: VCC→switch tube T1→head excitation coil W2→switch tube T4→current limiting resistor Ra (Ra=0.5Ω in the embodiment)→GND; send the voltage VR across the current limiting resistor Ra and the set voltage domain value VS (VS=0.2V in the embodiment) to the positive and negative input terminals of the voltage comparator, respectively.

[0040] ​S2, first flip-flop detection and current path switching: when the output level of the voltage comparator flips (from positive to negative or from negative to positive), the event is captured by the digital controller pin P1; the switch tube T1 and T4 are sent to the off driving signal, that is, QD14 is low; the switch tube T2 and T3 are sent to the on driving signal, that is, QD23 is high; the current time t1 is recorded, and TP=t1-t0 is calculated; the current path is switched to: VCC→switch tube T2→head excitation coil W2→switch tube T3→current limiting resistor Ra→GND; the voltage VR across the current limiting resistor Ra and the set voltage domain value VS are sent to the positive and negative input terminals of the voltage comparator, respectively.

[0041] S3, second flip-flop detection and current path recovery: when the output level of the voltage comparator flips again, the event is captured by the digital controller pin P1; the switch tube T2 and T3 are sent to the off driving signal, that is, QD23 is low; the switch tube T1 and T4 are sent to the on driving signal, that is, QD14 is high; the current time t2 is recorded, and TN=t2-t1 is calculated.

[0042] S4, feedback signal calculation and compensation current control: T=TP-TN is calculated, and T is sent to the digital PI controller in the CPU as a feedback signal; the output of the PI controller is used as the voltage driving signal of the compensation winding coil W3 of the zero-magnetic-flux direct-current current sensor; after being amplified by the power amplification unit, the driving signal acts on the compensation winding coil W3 to generate a compensation current; according to the current of the compensation winding coil W3 and the turns ratio (500:1 in this embodiment), the current of the primary measured current coil W1 is calculated.

[0043] S5, loop control and real-time current monitoring: repeat steps S1-S4 to obtain the current value of the primary measured current coil W1 in real time.

[0044] This embodiment is similar to embodiment 1, the primary measured current coil W1, the head excitation coil W2 and the compensation winding coil W3 are all wound on the same magnetic core; the on or off driving signal QD14 of the switch tube T1 and T4 is sent by the same pin P2 of the CPU; the on or off driving signal QD23 of the switch tube T2 and T3 is sent by the same pin P3 of the CPU; a digital voltage comparator is used for the voltage comparator to improve the anti-interference ability and precision of the system; when the voltage VR across the current limiting resistor Ra reaches the set voltage domain value VS, the head magnetic core enters the saturation state, thereby realizing effective control of the magnetic flux.

[0045] In the embodiment, by adjusting the resistance value of the current limiting resistor Ra and setting the voltage domain value VS, the measurement of different ranges of direct current can be realized; through the control method of the embodiment, the manufacturing complexity of the magnetic core probe is further simplified, and the sensitivity and measurement accuracy of the sensor are improved. At the same time, in the digital implementation, the use of high-precision AD sampling chips is avoided, and the system hardware cost and complexity are reduced. In the embodiment, when the primary measured direct current is 100 A and the turn ratio is 500:1, the system can stably and accurately output the compensation current corresponding to the primary measured current, thereby realizing high-precision measurement of the direct current.

Claims

1. A zero flux digital DC current sensor closed loop control method, characterized by: The method comprises the following steps: S1, initializing driving signals: sending on and off driving signals to two groups of switching tubes respectively, and starting a timer, the on or off driving signals of the two groups of switching tubes are sent by two pins of a CPU, and each group of switching tubes comprises two switching elements; S2, first flip detection: switching the on state of the switching tube according to the flip of the voltage comparator output level, and recording the timer time, the voltage comparator is used for comparing the voltage across the current limiting resistor with a set voltage domain value, and the voltage comparator is an analog voltage comparator or a digital voltage comparator; S3, second flip detection: calculating the time difference of the two timers, and taking the time difference as a feedback signal and sending the feedback signal into a digital PI controller; S4, calculating the feedback signal: the output of the digital PI controller is taken as a voltage driving signal of the compensation winding coil, and the current of the compensation winding coil multiplied by the turns ratio reflects the current of the primary measured current coil; S5, loop control: repeating the above steps S1-S4 to obtain the current value of the primary measured current coil in real time.

2. The zero flux digital DC current sensor closed loop control method of claim 1, wherein: The primary measured current coil, the head excitation coil and the compensation winding coil are all wound on the same magnetic core, and the head excitation coil is a single excitation winding.

3. The zero flux digital DC current sensor closed loop control method of claim 1, wherein: When the voltage across the current limiting resistor reaches the set voltage domain value, the head magnetic core enters a saturated state, at which time the voltage comparator output level flips.

4. The zero flux digital DC current sensor closed loop control method of claim 3, wherein: The flip of the voltage comparator output level refers to that the output changes from a positive maximum value to a negative maximum value, or from a negative maximum value to a positive maximum value.

5. The zero flux digital DC current sensor closed loop control method of claim 1, wherein: The product of the compensation winding current and the turns ratio is used to calculate the current of the primary measured current coil, wherein the turns ratio refers to the ratio of the number of turns of the compensation winding coil to the number of turns of the primary measured current coil.

6. The zero flux digital DC current sensor closed loop control method of claim 1, wherein: The digital PI controller adjusts the voltage driving signal of the compensation winding coil according to the feedback signal to realize accurate measurement of the current of the primary measured current coil.

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