B-type residual current intelligent protection device

Abstract

The invention provides a B-type residual current intelligent protection device. Common-mode interference caused by a magnetic core and an inverter circuit is counteracted by constructing an H-bridge inverter double-sampling resistor differential output circuit, a voltage comparison circuit and a driving circuit are constructed to enable the H-bridge inverter circuit to perform self-oscillation, and a high-low level time difference of an excitation square wave signal is extracted to calculate a measured current. The extraction of the digital signal improves the anti-interference capability and simplifies the circuit design. Synchronous extraction transformation is introduced through a Goertzel algorithm to analyze sampled residual current signal features in a time-frequency domain, residual current waveform feature values are extracted in several specific frequency domains, the recognition precision and speed are improved, and misjudgment is reduced. The requirements of a time difference method B-type residual current detection system of a self-excited oscillation fluxgate current sensor are met, the precision, the resolution ratio and other performance of the current sensor system are improved, and the requirements of high precision and low cost of the B-type residual current detection system are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of current sensors, and particularly relates to a type-B intelligent residual current protection device. Background Art

[0002] In the era of the rapid development of power electronics technology, the grid connection of solar power generation and electric vehicles in China is continuously developing, and frequency conversion equipment is widely used. Leakage refers to the leakage of current due to the insulation breakage of the line for some reasons. Electrical fires and personal electric shock accidents caused by improper use of electrical equipment or leakage of distribution lines occur frequently, posing a great threat to people's lives and property safety.

[0003] The power system in China uses 50Hz sinusoidal alternating current, and this rated frequency is also called the power frequency. When an electrical device leaks electricity, the frequency of its leakage current is mainly 50Hz. When some electrical appliances with frequency conversion functions leak electricity, high-frequency sinusoidal leakage currents with large amplitudes will be generated. Residual current mainly includes sinusoidal alternating current, pulsating direct current, and smooth direct current residual current, and its frequency range can reach 0 - 1000Hz, or even higher. The complexity of the spectra of different waveform residual currents is different. The spectra of sinusoidal alternating current and smooth direct current residual currents are relatively simple, while the spectrum of pulsating direct current residual current is relatively complex because the current waveform is distorted (non-sinusoidal waveform). In practice, pulsating direct current residual current is generated after a grounding fault occurs in a circuit containing a rectifier device. The current lag angles of typical pulsating direct current residual currents are 0°, 90°, and 135° respectively, and these three waveforms can be simply referred to as half-wave, 90° wave, and 135° wave. When leakage occurs in a circuit, sometimes there will be a situation of superposition of multiple waveforms. The IEC standard only stipulates corresponding regulations for three special composite waveforms, namely the composite wave of 50Hz alternating current superimposed with 0.4 times nI direct current, the composite wave of half-wave superimposed with 0.4 times nI direct current, and the composite residual current superimposed with 10Hz, 50Hz, and 1000Hz. In summary, the types of residual current are 50Hz sine wave residual current, pulsating direct current residual current, smooth direct current residual current, and composite wave.

[0004] According to the standards IEC / TR 60755-2008 formulated by IEC and the national standard GB_T_6829-2024, residual current operated protective devices can be divided into four types: AC type, A type, F type and B type according to the different ability to detect residual current. The AC type residual current operated protective device that can measure the 50Hz power frequency sinusoidal leakage current is widely used in China at present. The A type can correctly operate for AC residual current, pulsating DC residual current, smooth DC residual current, and AC superimposed DC residual current. The F type includes the functions of the A type and can also correctly operate for half-wave superimposed DC residual current. The B type not only includes the functions of the F type, but also can correctly operate for the composite wave residual current of 50Hz, 100Hz, and 1000Hz. Therefore, the B type is also called the full-current sensitive type residual current protective device.

[0005] The patent with the application number 202122452003.X and the name of B-type residual current operated circuit breaker realizes B-type residual current protection by connecting an integrating circuit, a filtering circuit and a bias adjustment circuit to the output of the sampling resistor. However, the overall circuit of this B-type residual current operated circuit breaker is relatively complex and requires a high-precision ADC, resulting in a large cost.

[0006] In the actual production process, the self-excited oscillation fluxgate current sensor is widely used in weak current detection due to its simple circuit, good sensitivity and strong anti-interference ability. The existing B-type residual current protection devices also choose the self-excited oscillation fluxgate current sensor as the signal acquisition component; Currently, the self-excited oscillation fluxgate current sensor generally adopts the scheme of H-bridge excitation core + sampling resistor detection.

[0007] For example, the patent with the application number CN202211412178.8 and the name of a digital fluxgate current sensor provides an excitation square wave through an H-bridge to saturate the core alternately, and collects the duty cycle of the excitation voltage to calculate the current. However, this scheme has the problem of insufficient DC interference suppression because a single sampling resistor cannot eliminate the inherent common-mode noise of the H-bridge.

[0008] The methods for calculating the primary current of the self-excited oscillation fluxgate current sensor include the average value method and the time difference method. The average value method usually connects a low-pass filter to the excitation output of the sampling resistor, then inputs it into the ADC of the MCU, and finally calculates its average value to calculate the magnitude of the primary current.

[0009] For example, in the patent with the application number CN202210673641.8 and the title of "A Fluxgate Current Sensor and a Current Measurement Method", the upper bridge arm of the H-bridge circuit is composed of PNP-type MOS transistors Q1 and Q2, and the lower bridge arm is composed of NPN-type MOS transistors Q3 and Q4. The output end of the lower bridge arm Q4 is connected to the positive end of the differential measurement resistor Re1, and the output end of the lower bridge arm Q3 is connected to the positive end of Re2. The negative ends of Re1 and Re2 are connected to the zero-potential reference point of the current sensor; the excitation detection circuit is also configured to equivalently convert the excitation current flowing through the excitation coil into the difference between two currents, and obtain the average value of the excitation current flowing through the excitation coil by the differential equivalent current, and then obtain the value of the primary DC current to be measured through the average value of the excitation current. The differential equivalent current is configured to eliminate the zero-point drift of the current sensor. However, the average current method is used to calculate the current. And because the magnetic core has inductance, for a sudden change in the excitation voltage signal, the excitation current cannot change suddenly and cannot be immediately reduced to 0. Therefore, the waveform after the subtraction circuit will be distorted. If the time difference method is used for calculation, there is no need to consider the waveform distortion, and only the flip of the excitation square wave needs to be sent to sample useful information. The residual current waveform required to be detected by the type B residual current protector is relatively complex. Common waveform recognition methods include the fast Fourier transform method. The Fourier transform can transform a signal from the time domain to the frequency domain. Therefore, the current waveform can be decomposed into its DC component, fundamental wave, and higher harmonics of each frequency. The FFT algorithm can achieve the purpose of accelerating the calculation speed. By periodicity and symmetry, the long sequence DFT is continuously decomposed into several short sequence DFTs, and the waveform is subjected to spectral analysis. According to the different proportions of the amplitudes of each harmonic, the residual current waveform is distinguished.

[0010] However, the FFT requires the number of sampling points to be 2^N, and the actual signal period may not be divisible by the number of sampling points, resulting in spectral leakage in the frequency domain after truncation and reducing the analysis accuracy; it is necessary to calculate all frequency domain components (including irrelevant harmonics), the algorithm has a high redundancy and poor real-time performance (especially for devices with limited MCU resources).

[0011] Although the differential resistor structure (Re1, Re2) can suppress part of the drift, it relies on the average current method. Due to the inductive characteristics of the magnetic core, the excitation current cannot change instantaneously when the square wave flips, and the output waveform of the subtraction circuit is distorted, affecting the measurement accuracy.

[0012] To improve the judgment accuracy of Type B residual current protectors, relevant algorithms are introduced to analyze the residual current waveform. For example, in the patent with the application number 202410474417.5 and the title "Control Method and Device for Type B Residual Current Protector", the sampled residual current is subjected to a fast Fourier transform, trained according to the characteristics of each frequency domain component in each residual current frequency domain, and input into the decision tree model to obtain the target waveform output by the decision tree model, so as to be able to process different waveforms. However, for the case where the sampling points are not 2^N, it may cause spectral leakage, and the energy of the true frequency component spreads to adjacent frequency points, affecting the amplitude accuracy. Calculating each frequency domain component in each residual current frequency domain not only increases the calculation amount but also has low efficiency. In practice, the presence of interference and clutter will also lead to misjudgment of the residual current.

[0013] Aiming at the defects existing in the prior art, the present invention selects a self-excited oscillation fluxgate current sensor as the signal acquisition component and designs a Type B residual current intelligent protection device based on the time difference method of the self-excited oscillation fluxgate current sensor. The time difference method calculates the magnitude of the primary current by obtaining the duration difference between the high and low levels on the excitation voltage. In contrast, the average value method has a more complex principle, higher cost, the analog signal is vulnerable to interference, and passing it through a low-pass filter will filter out the high-frequency information of the excitation signal, resulting in poor accuracy. At the same time, the Goertzel algorithm is used to analyze the residual current waveform, which has low calculation amount, high accuracy, is not limited by 2^N, can flexibly adapt to non-integer cycle sampling, and avoids the spectral leakage problem of FFT. Only the amplitudes of the 50Hz fundamental wave + a small amount of harmonics need to be detected, and combined with the waveform recognition algorithm, the target residual current can be detected. Summary of the Invention

[0014] The present invention proposes a Type B residual current intelligent protection device, aiming to realize the detection of complex residual current by the time difference method of the self-excited oscillation fluxgate current sensor, achieve the accurate and effective identification of complex residual current, and the intelligence of the system.

[0015] The present invention includes a self-excited oscillation fluxgate current sensor, an MCU main control module, and a power supply circuit. The self-excited oscillation fluxgate current sensor includes a circular magnetic core and a signal processing module. The signal processing module is connected to the circular magnetic core and the MCU main control module, and is used to generate a voltage excitation for the magnetic core and send an excitation voltage signal to the MCU main control module. The MCU main control module is used for sampling, processing the measured current signal, and controlling various peripherals; the power supply circuit is electrically connected to the signal processing module and the MCU main control module, and is used to supply power to the entire system; The toroidal magnetic core is connected to the signal processing module to generate an excitation current signal containing the information of the current to be measured. A primary winding and a secondary winding are wound around the toroidal magnetic core. The signal processing module includes a full-bridge inverter circuit, a first sampling resistor Rm1, a second sampling resistor Rm2, a differential amplifier circuit, a first voltage comparison circuit, a second voltage comparison circuit, a NAND gate, a D flip-flop, a limiting circuit, and a full-bridge drive circuit.

[0016] The toroidal magnetic core concentrates and guides the circular magnetic field generated by the conductor current to the secondary winding, generates an induced current signal, and superimposes it with the alternating current generated by applying a voltage excitation to the secondary winding to form an excitation current; the secondary winding is electrically connected to the full-bridge inverter circuit of the signal processing module; The full-bridge drive circuit in the signal processing module is connected to the full-bridge inverter circuit and is used to control the output of the full-bridge inverter circuit; the full-bridge inverter circuit applies a voltage excitation to the magnetic core to make it reach the saturation state. At the same time, the excitation current flows into two sampling resistors at both ends of the full-bridge inverter circuit respectively; the positive ends of the sampling resistors are connected to the differential amplifier circuit, the two output ends of the differential amplifier circuit are respectively connected to two voltage comparators, the output ends of the voltage comparators are connected to the NAND gate, and the output end of the NAND gate is connected to the CLK end of the D flip-flop; the output end of the D flip-flop is connected to the full-bridge drive circuit to control the flip of the full-bridge drive circuit, thereby controlling the full-bridge inverter circuit to make the magnetic core reach the alternating saturation state and suppressing the common-mode interference of the circuit.

[0017] The MCU main control module includes a digital signal processing DSP chip and a trip device.

[0018] The limiting circuit in the signal processing module limits the excitation current signal containing the information of the current to be measured collected by the toroidal magnetic core to 0~3.3V, and then inputs it into the ECAP acquisition pin of the DSP chip in the MCU main control module. The high and low level time difference is calculated by the positive and negative durations within one excitation voltage cycle, and the current to be measured is solved by the Goertzel algorithm. According to the characteristic analysis of the collected current data to be measured, the type of the residual current is judged and whether the operating current value is reached is judged, and the opening and closing of the trip device are controlled.

[0019] During the solution, the MCU analyzes from specific frequency domains through the Goertzel algorithm, judges the residual current waveform according to the amplitude characteristics and magnitudes of specific frequencies within one sampling period, classifies the frequency characteristics of the residual current under different conditions, and then calculates its effective value according to the sampled residual current value to judge whether it exceeds the threshold. When the magnitude of the residual current exceeds the threshold, the trip device is activated to trip.

[0020] Preferably, the material of the toroidal magnetic core is iron-based nanocrystalline.

[0021] Furthermore, the power supply circuit includes a regulated power supply and a reference voltage power supply.

[0022] Further, the MCU main control module further includes a display screen module, SIC communication, and a key circuit.

[0023] Preferably, the digital signal processing DSP chip is selected as the TMS320F28335 chip.

[0024] Further, the screen display module is selected from a dot matrix liquid crystal display screen, TFT, LCD display screen, or OLED display screen, and is used to display the code of the residual current fault type and the tripping time point of the tripping device.

[0025] Further, the historical record of the stored data is displayed through the keys. The historical record includes a set of key circuits including the code of the residual current fault type and the tripping time point of the tripping device. The three keys K1, K2, and K3 respectively perform the following functions: 1. Storage function: Pressing K1 stores the code of the residual current fault type into the EEPROM; 2. Deletion function: Pressing K2 deletes the stored data; 3. "Historical record display" function: Pressing K3 once will display the historical record, and each time K3 is pressed thereafter, the page number of the historical record displayed will increase until page 1 is returned.

[0026] Further, the SCI communication module is selected as the RS232 module, and serial communication is established with the host computer through SCI. According to the commands sent by the host computer received by the MCU, the collected primary side current signal, waveform discrimination type, and fault type are sent to the host computer in real time.

[0027] Further, in the signal processing circuit: The full-bridge inverter circuit is composed of 4 PNP-type MOS transistors. Among them, every two MOS transistors form a half-bridge, and the grounding end of each half-bridge is connected to the positive end of a sampling resistor, and the negative end of the sampling resistor is grounded.

[0028] The input ends of the differential amplifier circuit are respectively connected to the positive ends of the sampling resistors connected to each half-bridge.

[0029] The voltage comparison circuit includes two voltage comparators comp1 and comp2, and a NAND gate; the output voltage signals of the differential amplifier circuit are respectively input into the positive end of voltage comparator comp1 and the negative end of comp2. The negative input end of comp1 is connected to the reference voltage source +Vref, the positive input end of comp2 is connected to the reference voltage source -Vref, and the output ends of voltage comparators comp1 and comp2 are connected to the input end of the NAND gate.

[0030] The described drive circuit includes a D flip-flop and two full-bridge drivers. The output terminal of the NAND gate is connected to the D terminal of the D flip-flop. The D terminal of the D flip-flop is connected to the Qn terminal. The Q terminal and the Qn terminal are respectively connected to the input terminals of a full-bridge driver. The output terminals of the full-bridge drivers are respectively connected to a half-bridge, controlling the inversion of the excitation voltage and avoiding the abnormal conduction of the full-bridge inverter circuit.

[0031] In view of the deficiencies of traditional residual current protectors, such as strong sensitivity to common-mode interference, low accuracy in extracting leakage characteristics under complex waveforms, susceptibility of analog signals to interference, and complex circuits, the present invention constructs an H-bridge inverter dual-sampling resistor differential output circuit to cancel the common-mode interference brought by the magnetic core and the inverter circuit, constructs a voltage comparison circuit and a drive circuit to make the H-bridge inverter circuit self-oscillate, extracts the time difference between the high and low levels of the excitation square-wave signal to calculate the measured current, and the extraction of digital signals improves the anti-interference ability and simplifies the circuit design. The characteristic values of the residual current waveform are extracted in specific frequency domains through the Goertzel algorithm, improving the accuracy, speed of recognition and reducing misjudgment. By adding modules such as display, communication, and storage, the protection system is made safer and more controllable, facilitating maintenance and debugging by personnel. It meets the requirements of the time-difference method B-type residual current detection system for self-oscillating fluxgate current sensors, and also improves the performance such as the accuracy and resolution of the current sensor system, meeting the high-precision and low-cost requirements of the B-type residual current detection system. Description of the Drawings

[0032] Figure 1 Schematic diagram of the overall structure of the present invention; Figure 2 Circuit diagram of the signal processing module in the embodiment; Figure 3 Flowchart for residual current judgment; Figure 4 Circuit diagram of the power supply in the embodiment; Figure 5 Block diagram of the MCU main control module in the embodiment.

[0033] Figure 6 Simulation diagram of the magnetic core and signal processing circuit in the embodiment; Figure 7 Simulation results of the input and output of the differential amplifier circuit in the embodiment; Figure 8 Simulation results of the excitation voltage with residual current input in the embodiment; Figure 9 Logic diagram of the voltage comparison circuit. (a) is the output signal of the differential amplifier circuit, (b) is the output signal of the voltage comparator with the input reference voltage -Vref, (c) is the output signal of the voltage comparator with the input reference voltage +Vref, and (d) is the output signal of the NAND gate. Detailed Embodiment

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] As Figure 1 shown, a type B residual current intelligent protection device includes a self-excited oscillation fluxgate current sensor, an MCU main control module, and a power supply circuit; the self-excited oscillation fluxgate current sensor includes a toroidal magnetic core and a signal processing module. The signal processing module is connected to the toroidal magnetic core and the MCU main control module, and is used to generate a voltage excitation for the magnetic core and send an excitation voltage signal to the MCU main control module. The MCU main control module is used to sample and process the measured current signal and control various peripherals. The MCU main control module includes a digital signal processing DSP, a TFT display screen, a key circuit, an I2C EEPROM storage chip, an SCI communication module, and a trip device; the power supply circuit is electrically connected to the signal processing module and the MCU main control module, and is used to supply power to the entire system. The power supply circuit includes a regulated power supply and a reference voltage power supply.

[0036] The toroidal magnetic core is connected to the signal processing module to generate an excitation current signal containing the measured current information. In this embodiment, the material of the toroidal magnetic core is iron-based nanocrystalline. A primary winding (energized wire) and a secondary winding are wound on the toroidal magnetic core; the secondary winding is electrically connected to the full-bridge inverter circuit of the signal processing module. The signal processing module includes a full-bridge inverter circuit, a first sampling resistor Rm1, a second sampling resistor Rm2, a differential amplifier circuit, a first voltage comparison circuit, a second voltage comparison circuit, a NAND gate, a D flip-flop, a limiting circuit, and a full-bridge drive circuit.

[0037] The full-bridge drive circuit in the signal processing module is connected to the full-bridge inverter circuit and is used to control the output of the full-bridge inverter circuit; the full-bridge inverter circuit gives a voltage excitation to the magnetic core to make it reach the saturation state, and at the same time, the excitation current flows into two sampling resistors at both ends of the full-bridge inverter circuit respectively; the positive end of the sampling resistor is connected to the differential amplifier circuit, and the two output ends of the differential amplifier circuit are respectively connected to two voltage comparators. The output ends of the voltage comparators are connected to the NAND gate, and the output end of the NAND gate is connected to the CLK end of the D flip-flop; the output end of the D flip-flop is connected to the full-bridge drive circuit to control the flip of the full-bridge drive circuit, thereby controlling the full-bridge inverter circuit to make the magnetic core reach an alternating saturation state.

[0038] During use, the output voltage of the differential amplifier circuit is compared with the reference voltage of the voltage comparator in the voltage comparator. When the output voltage of the differential amplifier circuit reaches the reference voltage of the voltage comparator, the toroidal core reaches the positive / negative saturation state, the output of the voltage comparator flips, and the flip of the full-bridge drive circuit is controlled through the logical output of the NAND gate and the D flip-flop, so that the core reaches the alternating saturation state through the full-bridge inverter circuit. When the residual current is detected, because the toroidal core reaches the positive and negative saturation states at different times, the high and low level durations of the excitation voltage are also different, and the measured current is calculated based on the duty cycle information of the excitation voltage.

[0039] In this embodiment, a signal processing module as Figure 2 shown is adopted. The H-bridge drive circuit selects EG2104, with a dead time of 520 ns, VIHmin = 3 V, and VILmax = 0.8 V. The output is connected to a 100-ohm resistor in parallel with a diode to enable the MOS transistor to turn off quickly and reduce the loss during turn-off. Looking up the chip manual, Qg = 22 nC, Cg = Qg / VGE = 22 nC / 5.9 V = 3.7 nF. If VDD = 7 V and VGE = VDD - VDBooT = 7 V - 1.1 V = 5.9 V, the bootstrap capacitor C1 = Cg x 15 = 56 nF. The H-bridge switch circuit selects Si4946Bey, which contains two NMOSs. D1 and D2 are bootstrap diodes, and D3, D4, D6, and D7 are protection diodes, all using IN4007 diodes. The sampling resistor selects a thick-film non-inductive resistor, the differential amplifier chip selects INA828IDR, and the voltage comparator selects the AD790 chip with a maximum response time of 45 ns. CD74HCT74M96, a D flip-flop chip, is selected, and Q and Qn are respectively connected to different input IN terminals of EG2104. The voltage regulator circuit is composed of an NMOS, a 3.3-V zener diode, and a resistor, and outputs a 3.3-V regulated voltage when the input high voltage is greater than 3.3 V.

[0040] The limiter circuit in the signal processing module limits the excitation current signal containing the measured current information collected by the toroidal core to 0 - 3.3 V, and then passes it into the ECAP acquisition pin of the DSP in the MCU main control module. The measured current is calculated by calculating the time difference between the high and low levels based on the positive and negative durations within one excitation voltage cycle. The host computer calculates the time difference between the high and low levels based on the positive and negative durations of the excitation current signal collected by the toroidal core within one cycle and calculates the measured current.

[0041] As Figure 3As shown in the figure, during the calculation, the host computer analyzes from specific frequency domains through the Goertzel algorithm, judges the residual current waveform according to the amplitude characteristics and magnitudes of specific frequencies within a sampling period, classifies the frequency characteristics of the residual current under different conditions, and then calculates the effective value of the residual current based on the sampled residual current value to determine whether it exceeds the threshold. THD is "Total Harmonic Distortion", and numerically it is the ratio of the square root of the sum of the squares of the effective values of the harmonics (100Hz, 150Hz, 200Hz, 400Hz, 1KHz) calculated by the Goertzel algorithm to the effective value of the 50Hz fundamental wave, multiplied by 100%. When the magnitude of the residual current exceeds the threshold, the trip device is activated to trip. At the same time, the TFT display screen can display the type of the residual current (fault type), and the type code of the residual current can be stored through the key circuit and the EEROM storage chip. The DSP communicates with the PC through the SCI to collect the information of the residual current in real time, which is also convenient for maintenance personnel to repair.

[0042] In this embodiment, the power supply circuit as shown in Figure 4 is selected. The reference voltage source selects REF50xx to output +Vref, and +Vref and two 10kΩ resistors are connected in parallel to the inverting input terminal and the output terminal of the OPA735AIDBVR operational amplifier. The non-inverting input terminal is grounded to make the output voltage of the operational amplifier -Vref. The LM7805L-TA3-T chip is selected to convert 7V to 5V to supply power to the voltage comparator, operational amplifier, NAND gate, and D flip-flop. The TLV70025DDCR chip is selected to convert 7V to -5V to supply power to the operational amplifier. The 1117-3.3 chip is selected to convert +5V to +3.3V to supply power to the MCU circuit.

[0043] As shown in Figure 5 the figure, in this embodiment, the TMS320F28335 chip is selected as the digital signal processing DSP chip, which includes 6 ECAP sampling pins T1 - T6. The pulse waveform to be measured is input on the capture pins, and the capture module will capture the specified capture logic state, such as the rising edge and the falling edge. The capture unit records the time of the timer, and the time difference between two falling edges is the pulse period, that is, the pulse frequency. Similarly, the rising edge of the pulse can also be captured, and the time difference between the rising edge and the falling edge can be calculated to obtain the duty cycle. Therefore, the capture unit can be used to measure the pulse period and the width (duty cycle) of the pulse. In the case of a 150MHz system clock, the time resolution of the 32-bit time base is 6.67ns.

[0044] Take the arithmetic mean of the middle three values after arranging the excitation voltage time difference information collected from T1 - T6 by magnitude as the sampling value at this time. Then store the N sampling values in an array for Goertzel operation and update them in real - time by overwriting to obtain the real - time waveform characteristic value, thereby judging the waveform type. After judging the waveform, calculate its effective value based on the remaining current value of the sampling and determine whether it exceeds the threshold. If it exceeds the threshold continuously 5 times, the trip device will trip.

[0045] The TFT display lcd12864 shows the code of the remaining current fault type and the tripping time point of the trip device. The fault code is determined by the remaining current data sampled by the sensor in real - time and the off - state of the trip device. The fault code consists of three digits (xxx). From left to right, it represents: the trip device is off (0xx), the trip device is on (1xx), the remaining current is AC (x0x), DC (x1x), and the type of the remaining current. For example, if the trip device is in the off state and the remaining current is a composite wave, the fault code is 004.

[0046] Through the key, the historical record of the stored data can be displayed. The historical record includes a set of key circuits stored, including the code of the remaining current fault type and the tripping time point of the trip device. There are three keys K1, K2, and K3, which respectively perform the following functions: 1. Storage function: Press K1 to store the code of the remaining current fault type into the EEPROM. In this implementation, the AT24C02 chip is selected; 2. Delete function: Press K2 to delete the stored data; 3. "Historical record display" function: Press K3 once to display the historical record. After that, each time K3 is pressed, the page number of the historical record displayed will increase until it returns to page 1. The SCI serial port selects the RS232 module and establishes serial communication with the PC through the SCI serial port. According to the commands sent by the PC received by the MCU, the primary current signal, waveform discrimination type, and fault type collected can be sent to the PC in real - time, which is convenient for maintenance personnel to repair and debug.

[0047] To demonstrate the effectiveness of the type - B residual current intelligent protection device in this embodiment, use the Figure 6 shown magnetic core and signal processing circuit simulation circuit for simulation on the Saber software. Use a non - linear transformer model to represent the magnetic core, and successively input parameters such as the B - H curve, shape, inner and outer diameters of the magnetic core. The winding ratio is 1:60, and the copper wire diameter is 0.35mm. P1 and m1 are the primary windings of the magnetic core, with the number of windings being 1, and are connected to the remaining current source. P2 and m2 are the secondary windings of the magnetic core, with the number of windings being 60, and are connected to the output terminal of the full - bridge inverter circuit. To improve the driving ability of the excitation voltage, Figure 1The full-bridge inverter circuit is composed of four switch-pa switches and two inverters. By controlling the conduction and turn-off of the switches, an excitation voltage is applied to the magnetic core. The excitation currents in different directions flow through the sampling resistors r1 and r2 in different directions and then ground. The labels n_1, n_2, n_419, n_420, and n_724 are the signal lines of this wire.

[0048] The waveforms on the sampling resistors (the waveforms of the input and output of the differential amplifier circuit) as shown Figure 7 are obtained through simulation; First, assume that when Q outputs a high level, switch-pa1 and switch-pa4 are conducting, and switch-pa2 and switch-pa3 are turned off. At this time, the m2 terminal of the magnetic core is at a high level, and the P2 terminal is at a low level. The direction of the excitation current is switch-pa1 - m2 - P2 - switch-pa4 - RS2 - GND. When Q is at a low level, switch-pa2 and switch-pa3 are conducting, and switch-pa1 and switch-pa4 are turned off. At this time, the P2 terminal of the magnetic core is at a high level, and the m2 terminal is at a low level. However, instantaneously, due to the inductance of the magnetic core, the direction of the excitation current cannot change suddenly, and the excitation current on RS2 will not immediately become 0. After that, the direction of the excitation current is switch-pa1 - m2 - P2 - switch-pa4 - RS2 - GND. The commutation of the full-bridge inverter circuit is achieved.

[0049] The signal n_419 is the excitation signal on the sampling resistor r2, and the signal n_420 is the excitation signal on the sampling resistor r1. The signal in n_419 is the duration of the high level of the excitation voltage. During this period, the magnetic core completes the transition from positive saturation to negative saturation. At time t2, the level of the excitation voltage flips. The signal in n_420 is the duration of the low level of the excitation voltage. During this period, the magnetic core completes the transition from negative saturation to positive saturation. It can be seen from the figure that due to the inductance of the magnetic core, the direction of the excitation current does not depend on the direction of the excitation voltages on both sides. When the excitation voltage flips, the two MOS transistors at the primary side are cut off, and the current starts to decay, but the direction temporarily remains the original direction for a period of time, and then drops to 0 and flows in the reverse direction to another sampling resistor. Therefore, it can be seen that the voltage amplitudes on the two sampling resistors are one large and one small, and the phases differ by 180°. If there is a common-mode interference between the H-bridge and the magnetic core, the voltage signals on the two sampling resistors can be differentially output to cancel the interference of the common-mode signal. Since the signals on the two sampling resistors are not perfectly connected in actual differential operation, spikes will appear at the subtraction of the positive and negative amplitudes, resulting in distortion. It is not suitable for the average value method, while the time difference method only cares about the flipping moment of the excitation voltage and will not affect the result.

[0050] The differential output voltage signals are respectively input into the positive terminal of voltage comparator U2 and the negative terminal of U3, and are compared with +Vref and -Vref respectively. The output terminals of U2 and U3 are connected to a NAND gate, so that when any one of the voltage comparators outputs a falling edge signal, a rising edge signal is output, and when any one of the voltage comparators outputs a rising edge signal, a falling edge signal is output. The output of the NAND gate is connected to the D terminal of a D flip-flop. The D terminal of the D flip-flop is connected to the Qn terminal. The Q and Qn terminals respectively control switch-pa1, switch-pa2 and switch-pa3, switch-pa4 of the full-bridge inverter circuit. When a high-level pulse occurs at the D terminal, the Q and Qn terminals of the D flip-flop can cause the phase of the full-bridge inverter circuit to flip.

[0051] As Figure 8 shown, it is the simulation result of the n_1 signal line (the excitation voltage on the excitation winding) when the residual current is input. From bottom to top are the simulation results of the residual current of 0A, +5A and -5A. DeltaX is the difference result of the abscissa X1 and X2, and the unit is μs. It can be seen that the frequency of the excitation voltage is basically unchanged at 2kHz. When the residual current is 0A, DeltaX is 251.26us, which is half of the period. When the residual current is +5A, DeltaX is 240.19us. When the residual current is -5A, DeltaX is 264.37us. When the residual current source outputs positive direct current, the time for the excitation current to reach positive saturation will decrease, so the high-level duration of the excitation voltage will also decrease. Correspondingly, the time for the excitation current to reach negative saturation will increase, so the low-level duration of the excitation voltage will also increase. Therefore, the duty cycle of the excitation voltage will decrease, and correspondingly, the difference between the high-level and low-level durations is negative. When the residual current source outputs negative direct current, the duty cycle of the excitation voltage will increase, and correspondingly, the difference between the high-level and low-level durations is positive. Therefore, the magnitude and direction of the residual current can be calculated according to the difference between the high-level and low-level durations of the excitation voltage. When the residual current source outputs alternating current or other relatively complex residual currents, since the frequency of the excitation voltage is 2kHz, which is much greater than the residual current signal of the 50Hz power frequency, the residual current signal sampled by each excitation voltage can be regarded as direct current, and the residual current can be approximated.

[0052] As Figure 9As shown, when the output signal of the differential amplifier circuit reaches +Vref, the negative input terminal of the voltage comparator in (c) is greater than +Vref at the positive input terminal, so the output is low level. The positive input terminal of the voltage comparator in (b) is greater than -Vref at the negative input terminal at this time, and the output remains high level. The NAND gate in (d) outputs a rising edge once, and the D flip-flop toggles once, and the excitation voltage signal toggles. At this time, the excitation current on the sampling resistor starts to decrease. When the negative input terminal of the voltage comparator in (c) is less than +Vref at the positive input terminal, the output is high level, and the output of the voltage comparator in (b) remains high level unchanged. At this time, the NAND gate in (d) outputs a falling edge once, and the D flip-flop is locked. When the output signal of the differential amplifier circuit reaches -Vref, similarly, the D flip-flop toggles once, and the excitation voltage signal toggles.

[0053] Although the specific embodiments of the present invention are as described above, the above content is only for facilitating the understanding of the present invention and is the specific embodiments adopted. Obviously, the above specific embodiments are only exemplary, and the details of the above embodiments are not limited in specific research. Therefore, those skilled in the art within the technical field of the present invention can make references and modifications in the form and details of the specific implementation without departing from the spirit and scope disclosed by the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. An intelligent residual current protection device of type B, comprising a self-excited oscillation fluxgate current sensor, an MCU main control module and a power supply circuit, wherein the self-excited oscillation fluxgate current sensor includes a toroidal magnetic core and a signal processing module; characterized in that: The signal processing module is connected to the toroidal magnetic core and the MCU main control module, and is used to generate voltage excitation for the magnetic core and send an excitation voltage signal to the MCU main control module; the MCU main control module is used to sample the excitation voltage signal, process the measured current signal, and control various peripherals; the power supply circuit is electrically connected to the signal processing module and the MCU main control module, and is used to supply power to the entire system; The toroidal magnetic core is connected to the signal processing module, generates an excitation current signal containing the measured current information, and the primary winding and the secondary winding are wound on the toroidal magnetic core; the secondary winding is connected to the full-bridge inverter circuit of the signal processing module; the signal processing module includes a full-bridge inverter circuit, a first sampling resistor Rm1, a second sampling resistor Rm2, a differential amplifier circuit, a first voltage comparison circuit, a second voltage comparison circuit, a NAND gate, a D flip-flop, a limiting circuit, and a full-bridge drive circuit; The full-bridge drive circuit in the signal processing module is connected to the full-bridge inverter circuit and is used to control the output of the full-bridge inverter circuit; the full-bridge inverter circuit applies voltage excitation to the magnetic core to make it reach the saturation state, and at the same time, the excitation current flows into two sampling resistors at both ends of the full-bridge inverter circuit respectively; the positive end of the sampling resistor is connected to the differential amplifier circuit, and the two output ends of the differential amplifier circuit are respectively connected to two voltage comparators, the output ends of the voltage comparators are connected to the NAND gate, and the output end of the NAND gate is connected to the CLK end of the D flip-flop; the output end of the D flip-flop is connected to the full-bridge drive circuit to control the flip of the full-bridge drive circuit, thereby controlling the full-bridge inverter circuit to make the magnetic core reach the alternating saturation state, and at the same time suppressing the common-mode interference of the circuit; The MCU main control module includes a digital signal processing DSP chip and a trip device; The limiting circuit in the signal processing module limits the excitation voltage signal containing the measured current information to 0~3.3V, and then passes it into the ECAP acquisition pin of the DSP chip in the MCU main control module. The high and low level time difference is calculated by the positive and negative durations within one excitation voltage cycle to calculate the measured current. The Goertzel algorithm is used to perform feature analysis on the collected measured current data to judge the type of residual current, and finally judge whether the operating current value is reached to control the opening and closing of the trip device; During the calculation, the MCU analyzes from specific frequency domains through the Goertzel algorithm, judges the residual current waveform according to the amplitude characteristics and magnitudes of specific frequencies within one sampling period, classifies the frequency characteristics of the residual current under different conditions, and then calculates the effective value of the sampled residual current according to the waveform to judge whether it exceeds the threshold; when the magnitude of the residual current exceeds the threshold, the trip device is activated to trip.

2. The Type B residual current intelligent protection device according to claim 1, wherein: The material of the toroidal magnetic core described above is iron-based nanocrystalline.

3. The Type B residual current intelligent protection device according to claim 1, characterized in that: The power supply circuit described above includes a regulated power supply and a reference voltage power supply.

4. The intelligent residual current protection device of type B according to claim 1, characterized in that: The MCU main control module described above further includes a display screen module, a storage module, an SCI communication module, and a key circuit.

5. The intelligent residual current protection device of type B according to claim 1, characterized in that: The digital signal processing DSP chip described above selects the TMS320F28335 chip.

6. The Type B residual current intelligent protection device according to claim 4, characterized in that: The screen display module described above selects a dot matrix liquid crystal display screen, a TFT, an LCD display screen, or an OLED display screen, and is used to display the code of the residual current fault type and the tripping time point of the trip device.

7. The Type B intelligent residual current protection device according to claim 4, characterized in that: The history of the stored data is displayed through the said button. The history includes a set of key circuits where the codes of the residual current fault types and the tripping time points of the release are stored. There are three buttons, K1, K2, and K3, which respectively perform the following functions:

1. Storage function: Pressing K1 stores the code of the residual current fault type in the EEPROM.

2. Delete function: Pressing K2 deletes the stored data.

3. "History display" function: Pressing K3 once displays the history. After that, each time K3 is pressed, the page number of the history display will increase until page 1 is returned.

8. The Type B residual current intelligent protection device according to claim 4, characterized in that: The selected SCI communication module is an RS232 module, which establishes serial communication with the host computer through SCI, and sends the collected primary side current signal, waveform discrimination type, and fault type to the host computer in real time according to the commands received by the MCU from the host computer.

9. The B-type residual current intelligent protection device according to claim 1, characterized in that: In the said signal processing circuit: The full-bridge inverter circuit is composed of 4 PNP-type MOS transistors. Among them, every two MOS transistors form a half-bridge. The grounding end of each half-bridge is connected to the positive end of a sampling resistor, and the negative end of the sampling resistor is grounded. The input ends of the differential amplification circuit are respectively connected to the positive ends of the sampling resistors connected to each half-bridge. The voltage comparison circuit includes two voltage comparators comp1 and comp2, and a NAND gate. The output voltage signals of the differential input amplification circuit are respectively input into the positive input end of voltage comparator comp1 and the negative input end of comp2. The negative input end of comp1 is connected to the reference voltage source +Vref, and the positive input end of comp2 is connected to the reference voltage source -Vref. The output ends of voltage comparators comp1 and comp2 are connected to the input end of the NAND gate. The drive circuit includes a D flip-flop and two full-bridge drivers. The output end of the NAND gate is connected to the D end of the D flip-flop. The D end of the D flip-flop is connected to the Qn end. The Q end and the Qn end are respectively connected to the input ends of a full-bridge driver. The output ends of the full-bridge drivers are respectively connected to a half-bridge to control the inversion of the excitation voltage and avoid abnormal conduction of the full-bridge inverter circuit.

Images