Self-oscillation type zero-flux current transformer and ripple elimination method thereof

Abstract

The invention discloses a self-oscillation type zero-flux current transformer and a ripple elimination method thereof, and the method comprises the steps: the zero-flux current transformer comprises a first DC magnetic modulation coil T1, a second DC magnetic modulation coil T2, an intermediate-frequency AC coil T3, a high-frequency AC coil T4 and a circuit module; the first direct-current magnetic modulation coil T1 comprises a first direct-current magnetic modulation coil iron core C1, a first direct-current magnetic modulation coil excitation winding W1 and a first section of secondary winding Ws; the second direct-current magnetic modulation coil iron core T2 comprises a second direct-current magnetic modulation coil iron core C2, a second direct-current magnetic modulation coil excitation winding W2 and a second section of secondary winding Ws; the first direct-current magnetic modulation coil excitation winding W1 and the second direct-current magnetic modulation coil excitation winding W2 have the same number of turns and are uniformly and densely wound on the circumferences of the first direct-current magnetic modulation coil iron core C1 and the second direct-current magnetic modulation coil iron core C2 respectively.

Description

Technical Field

[0001] The present invention relates to the technical field of current transformers, and more particularly to a self-excited oscillation type zero magnetic flux current transformer and a method for eliminating ripples thereof. Background Art

[0002] Zero-flux current transformers are widely used in high-accuracy AC and DC current measurement scenarios in the fields of power, industry, railways, and medical treatment. Due to their high precision, fast response, and wide bandwidth, they effectively ensure the smooth, accurate, and high-performance application of electrical control systems.

[0003] The zero flux current transformer is mainly composed of two parts: DC measurement and AC measurement. AC measurement mainly relies on active compensation current transformers, and the technology is relatively mature. The core principle of DC measurement is fluxgate technology. Its zero flux detector is two anti-phase symmetrical iron core windings connected in series. The two symmetrical iron cores are excited by square waves, triangle waves or sine waves. The demodulation circuit senses the even harmonics generated by the DC flux of the primary winding, and drives the operational amplifier to excite the secondary winding to generate DC compensation current to reach the zero flux state of DC ampere-turn balance. The magnitude of the secondary DC current can accurately reflect the magnitude of the primary DC current.

[0004] Traditional zero-flux mutual inductors need to generate an excitation signal of a certain frequency through a crystal oscillator, and then demodulate it through a complex phase-sensitive demodulation circuit or a peak-difference demodulation circuit to obtain the measured DC signal. The circuit technology of its excitation demodulation scheme is complex, and the cost and energy consumption are high, which has become one of the problems restricting the promotion and application of zero-flux technology.

[0005] At the same time, the DC obtained by demodulation inevitably brings ripples, and for high-frequency measurements, the ripple current is equivalent to a certain internal harmonic disturbance. The ripple caused by the asymmetry of the magnetic properties of the iron core is called induction ripple, and the ripple caused by electronic parts such as the excitation circuit and demodulation circuit is called modulation ripple. The size of the ripple will affect the effect of DC measurement. Therefore, reducing the ripple has become one of the difficulties of fluxgate technology. Summary of the invention

[0006] According to the present invention, a self-excited oscillation zero-flux current transformer is provided to solve the technical problems that the excitation demodulation scheme of the traditional zero-flux current transformer is complex in circuit technology, high in cost and energy consumption, and the DC obtained by demodulation inevitably brings ripples.

[0007] According to a first aspect of the present invention, there is provided a self-excited oscillation type zero-flux current transformer, comprising:

[0008] The zero flux current transformer comprises a first DC magnetic modulation coil T1, a second DC magnetic modulation coil T2, a medium frequency AC coil T3, the high frequency AC coil T4 and a circuit module;

[0009] The first DC magnetic modulation coil T1 includes a first DC magnetic modulation coil core C1, a first DC magnetic modulation coil excitation winding W1 and a first secondary winding W s The second DC magnetic modulation coil core T2 includes a second DC magnetic modulation coil core C2, a second DC magnetic modulation coil excitation winding W2 and a second secondary winding W s ;

[0010] The first DC magnetic modulation coil excitation winding W1 and the second DC magnetic modulation coil excitation winding W2 have the same number of turns and are evenly and densely wound on the circumference of the first DC magnetic modulation coil core C1 and the second DC magnetic modulation coil core C2 respectively.

[0011] Optionally, the medium frequency AC coil T3 includes a medium frequency AC coil core C3, a medium frequency AC coil detection winding W3 and a third section secondary winding W s ;

[0012] The medium frequency AC coil detection winding W3 is evenly and densely wound on the circumference of the medium frequency AC coil core C3;

[0013] The intermediate frequency AC winding core C3 surrounds the first DC magnetic modulation winding core C1 and the second DC magnetic modulation winding core C2. In addition to serving as an intermediate frequency signal sensing core, the intermediate frequency AC winding core C3 also serves as a magnetic shield for the first DC magnetic modulation winding core C1 and the second DC magnetic modulation winding core C2.

[0014] Optionally, the high-frequency AC coil T4 includes a high-frequency AC coil core C4, a high-frequency AC coil detection winding W4 and a fourth secondary winding W s ;

[0015] The high-frequency AC coil detection winding W4 is evenly and densely wound on the circumference of the high-frequency AC coil core C4;

[0016] The intermediate frequency AC coil core C3 surrounds the high frequency AC coil core C4 and serves as a magnetic shield for the high frequency AC coil core C4 in addition to being a intermediate frequency signal sensing core.

[0017] Optionally, the zero flux current transformer further includes a primary winding W p , primary winding W p It is a turn of through-core conductor, passing through the central apertures of the first DC magnetic modulation coil T1, the second DC magnetic modulation coil T2, the medium frequency AC coil T3 and the high frequency compensation coil T4;

[0018] Secondary winding W sIt is evenly and densely wound on the circumference of the whole coil package composed of the first DC magnetic modulation coil package T1, the second DC magnetic modulation coil package T2, the medium frequency AC coil package T3 and the high frequency compensation coil package T4.

[0019] Optionally, the circuit module includes a self-excited oscillator, a low-pass filter, a band-pass filter, a high-pass filter, an intermediate frequency signal amplifier, a high-frequency signal amplifier, a power amplifier and a load resistor;

[0020] The self-excited oscillator includes a first threshold voltage setting resistor R1, a second threshold voltage setting resistor R2, a first excitation current sampling resistor R3, a second excitation current sampling resistor R4, and a comparator.

[0021] Optionally, the first DC magnetic modulation coil core C1 and the first DC magnetic modulation coil excitation winding W1 constitute a nonlinear inductor L1, the second DC magnetic modulation coil core C2 and the second DC magnetic modulation coil excitation winding W2 constitute a nonlinear inductor L2, and the self-excited oscillator and the nonlinear inductors L1 and L2 constitute a self-excited oscillation circuit.

[0022] Optionally, the negative input end of the comparator is respectively connected to the first excitation current sampling resistor R3 and the non-polarity end of the first DC magnetic modulation coil excitation winding W1, the other end of the first excitation current sampling resistor R3 is grounded, the positive input end of the comparator is respectively connected to one end of the first threshold voltage setting resistor R1 and the second threshold voltage setting resistor R2, one end of the second threshold voltage setting resistor R2 is grounded, the other end of the second threshold voltage setting resistor R2 is connected to the polarity end of the first DC magnetic modulation coil excitation winding W1, the output end of the comparator is connected to the non-polarity end of the second DC magnetic modulation coil excitation winding W2, the polarity end of the second DC magnetic modulation coil excitation winding W2 is connected to one end of the second excitation current sampling resistor R4, the other end of the second excitation current sampling resistor R4 is grounded, the output end of the comparator is simultaneously connected to the input end of the low-pass filter, the non-polarity end of the intermediate frequency AC coil detection winding W3 is connected to the band-pass filter, and the non-polarity end of the high frequency AC coil detection winding W4 is connected to the high-pass filter;

[0023] The output voltage signal of the low-pass filter is added to the output voltage of the band-pass filter and connected to the front end of the intermediate frequency signal amplifier; the front end of the high-frequency signal amplifier is connected to the voltage output end of the high-pass filter, the output voltage signal of the tail end is added to the output voltage of the high-frequency signal amplifier and connected to the front end of the power amplifier, and the tail end of the power amplifier is connected to the secondary winding W s Polarity end connection, load resistance and secondary winding W s Non-polar end connection.

[0024] Optionally, the self-excited oscillation circuit is in different working states, and the comparator output alternately changes between two limit levels ±U with time. s, assuming that the initial comparator positive input voltage U p >Comparator negative input voltage U n At this time, the comparator outputs the forward limit voltage U s , and U p =U s *R1 / (R1+R2), comparator output voltage U s Acting on the nonlinear inductance L1 of the first DC magnetic modulation coil exciting winding W1, the excitation current I in the nonlinear inductance L1 ex1 Starting from zero, the voltage U on the excitation current sampling resistor R3 in the same circuit increases. n will also increase when its voltage increases to U n >U p When the comparator output turns to the negative limit voltage -U s , and U p =﹣U s *R1 / (R1+R2), -U s Acting on the nonlinear inductance L1 of the excitation winding W1, the excitation current I ex1 The voltage U on the first excitation current sampling resistor R3 in the same circuit decreases to a negative value. n It will also decrease to a negative value when its voltage increases to U n p When the comparator outputs the forward limit voltage U s Due to the symmetry of the excitation performance of the core T1, the comparator will continuously output a forward voltage U at fixed periods t1 and t2. s and forward voltage -U s , that is, the period is t1+t2 and the amplitude is U s square wave signal.

[0025] Optionally, the self-excited oscillation circuit, when the primary winding W p When a DC current flows through the core, the symmetry of the core excitation performance is destroyed, resulting in a bias proportional to the DC current, which causes the comparator to output a forward limit voltage U s And negative limit voltage ﹣U s The time of inconsistency t1≠t2, and the degree of inconsistency Δt is proportional to the DC flowing in the primary winding;

[0026] The comparator outputs a square wave signal to excite the two reversely connected first DC magnetic modulation coils T1 and second DC magnetic modulation coils T2, so that the same excitation generates magnetic fluxes in the first DC magnetic modulation coils T1 and second DC magnetic modulation coils T2 with equal magnitude and opposite directions, thereby canceling each other out;

[0027] ​The low-pass filter filters the high-frequency signal of the square wave voltage signal output by the comparator and directly converts it into a corresponding DC voltage signal;

[0028] The bandpass filter filters the low-frequency and high-frequency parts of the AC voltage signal induced in the intermediate frequency AC coil detection winding W3, and amplifies and outputs the intermediate frequency AC voltage small signal and the DC voltage small signal through the intermediate frequency amplifier;

[0029] The high-pass filter filters the low-frequency part of the AC voltage signal induced in the high-frequency AC coil detection winding W4, and then amplifies the high-frequency AC voltage small signal through the high-frequency amplifier for output.

[0030] Optionally, the power amplifier further amplifies the voltage signal to drive the secondary winding and the load resistor to output a secondary current;

[0031] The load resistor converts the current signal into a voltage signal;

[0032] The second DC magnetic modulation coil excitation winding W s When ripple current appears in the high-frequency AC coil T4, its ripple magnetic flux will generate an induced potential on the high-frequency AC coil detection winding W4 of the high-frequency induction coil, and drive the high-frequency signal amplifier and the power amplifier to generate an anti-phase current in the secondary winding to offset the ripple and high-frequency harmonics until the ripple magnetic flux induced in the high-frequency AC coil T4 is zero.

[0033] According to another aspect of the present invention, there is also provided a method for eliminating ripples according to a zero flux current transformer, comprising:

[0034] By adding high-frequency coils and negative feedback circuits to offset the ripple and high-frequency interference generated by the system, when the secondary winding W s When there is ripple current I r , according to Ampere's circuit law:

[0035]

[0036] Among them, H r is the magnetic field strength of the core C4, N2 is the number of turns of the secondary winding, and l is the average magnetic path length of the core C4;

[0037] According to the magnetic properties of the iron core, there are:

[0038] B=μH r (2)

[0039] Wherein, μ is the magnetic permeability of the core C4;

[0040] Φ=BS (3)

[0041] Wherein, S is the cross section of the core C4;

[0042] According to the law of electromagnetic induction, the ripple magnetic flux φ generates an induced potential U on the detection winding W4 of the high-frequency induction coil. r , and drives the high-frequency signal amplifier and the power amplifier to generate the reverse ripple current I in the secondary winding r ', to offset the ripple current I r , until the ripple flux induced in coil T4 is zero, that is,

[0043] I r =I r ' (4).

[0044] Therefore, when the zero flux current transformer adopts phase-sensitive demodulation, the system ripple is mainly modulation ripple; when the zero flux current transformer adopts peak difference demodulation, the system ripple includes inductive ripple and modulation ripple. Regardless of the sampling excitation demodulation method, a complex crystal oscillator excitation and demodulation circuit is required. At the same time, the existing zero flux transformer generally adopts a three-core four-winding structure. The inductive ripple and modulation ripple are amplified by the signal amplifier and the power amplifier and output to the secondary winding, and cannot be simply eliminated by the filtering circuit, because when there is a high-frequency signal in the primary, the secondary cannot normally respond to the waveform of the primary signal after filtering. The self-excited oscillation circuit does not allow the crystal oscillator to generate high-frequency signal oscillation excitation. At the same time, its demodulation circuit is a simple low-pass filter circuit that is easy to implement. At the same time, a high-frequency induction coil T4 is added. Through negative feedback and zero flux principles, the secondary can accurately sense the primary high-frequency signal, and at the same time greatly offset the ripple signal generated inside the system, so as to achieve the effect of significantly reducing the system ripple interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0046] Figure 1 This is a structural principle diagram of the self-excited oscillation type zero-flux current standard described in this embodiment;

[0047] Figure 2 is a cross-sectional structural diagram of the side of the self-excited oscillation type zero-flux current standard described in this embodiment;

[0048] Figure 3 This is a DC core excitation curve diagram described in this embodiment;

[0049] Among them, T1-first DC magnetic modulation coil, T2-second DC magnetic modulation coil, T3-medium frequency AC coil, T4-high frequency AC coil, C1-first DC magnetic modulation coil core, C2-second DC magnetic modulation coil core, C3-medium frequency AC coil core, C4-high frequency AC coil core, W1-first DC magnetic modulation coil excitation winding, W2-second DC magnetic modulation coil excitation winding, W3-medium frequency AC coil detection winding, W4-high frequency AC coil detection winding, W p -Primary winding, W s -secondary winding, R1-first threshold voltage setting resistor, R2-second threshold voltage setting resistor, R3-first excitation current sampling resistor, R4-second excitation current sampling resistor, I p -Primary current, I s -Secondary current, I ex1 -T1 coil excitation current, I ex2 -T2 coil excitation current, U p -Comparator positive input voltage, U n -Comparator negative input voltage, U s -Comparator output voltage, U dc -Low-pass filter output DC voltage, U acm -Intermediate frequency signal amplifier outputs intermediate frequency AC voltage, U ach -High frequency signal amplifier outputs high frequency AC voltage, I dc -Primary DC current, I s -Secondary current. DETAILED DESCRIPTION

[0050] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0051] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0052] According to a first aspect of the present invention, there is provided a self-excited oscillation type zero flux current transformer, comprising:

[0053] The zero flux current transformer comprises a first DC magnetic modulation coil T1, a second DC magnetic modulation coil T2, a medium frequency AC coil T3, the high frequency AC coil T4 and a circuit module;

[0054] The first DC magnetic modulation coil T1 includes a first DC magnetic modulation coil core C1, a first DC magnetic modulation coil excitation winding W1 and a first secondary winding W s The second DC magnetic modulation coil core T2 includes a second DC magnetic modulation coil core C2, a second DC magnetic modulation coil excitation winding W2 and a second secondary winding W s ;

[0055] The first DC magnetic modulation coil excitation winding W1 and the second DC magnetic modulation coil excitation winding W2 have the same number of turns and are evenly and densely wound on the circumference of the first DC magnetic modulation coil core C1 and the second DC magnetic modulation coil core C2 respectively.

[0056] Optionally, the medium frequency AC coil T3 includes a medium frequency AC coil core C3, a medium frequency AC coil detection winding W3 and a third section secondary winding W s ;

[0057] The medium frequency AC coil detection winding W3 is evenly and densely wound on the circumference of the medium frequency AC coil core C3;

[0058] The intermediate frequency AC winding core C3 surrounds the first DC magnetic modulation winding core C1 and the second DC magnetic modulation winding core C2. In addition to serving as an intermediate frequency signal sensing core, the intermediate frequency AC winding core C3 also serves as a magnetic shield for the first DC magnetic modulation winding core C1 and the second DC magnetic modulation winding core C2.

[0059] Optionally, the high-frequency AC coil T4 includes a high-frequency AC coil core C4, a high-frequency AC coil detection winding W4 and a fourth secondary winding W s ;

[0060] The high-frequency AC coil detection winding W4 is evenly and densely wound on the circumference of the high-frequency AC coil core C4;

[0061] The intermediate frequency AC coil core C3 surrounds the high frequency AC coil core C4 and serves as a magnetic shield for the high frequency AC coil core C4 in addition to being a intermediate frequency signal sensing core.

[0062] Optionally, the zero flux current transformer further includes a primary winding W p , primary winding W p It is a turn of through-core conductor, passing through the central apertures of the first DC magnetic modulation coil T1, the second DC magnetic modulation coil T2, the medium frequency AC coil T3 and the high frequency compensation coil T4;

[0063] Secondary winding W s It is evenly and densely wound on the circumference of the whole coil package composed of the first DC magnetic modulation coil package T1, the second DC magnetic modulation coil package T2, the medium frequency AC coil package T3 and the high frequency compensation coil package T4.

[0064] Optionally, the circuit module includes a self-excited oscillator, a low-pass filter, a band-pass filter, a high-pass filter, an intermediate frequency signal amplifier, a high-frequency signal amplifier, a power amplifier and a load resistor;

[0065] The self-excited oscillator includes a first threshold voltage setting resistor R1, a second threshold voltage setting resistor R2, a first excitation current sampling resistor R3, a second excitation current sampling resistor R4, and a comparator.

[0066] Optionally, the first DC magnetic modulation coil core C1 and the first DC magnetic modulation coil excitation winding W1 constitute a nonlinear inductor L1, the second DC magnetic modulation coil core C2 and the second DC magnetic modulation coil excitation winding W2 constitute a nonlinear inductor L2, and the self-excited oscillator and the nonlinear inductors L1 and L2 constitute a self-excited oscillation circuit.

[0067] Optionally, the negative input end of the comparator is respectively connected to the first excitation current sampling resistor R3 and the non-polarity end of the first DC magnetic modulation coil excitation winding W1, the other end of the first excitation current sampling resistor R3 is grounded, the positive input end of the comparator is respectively connected to one end of the first threshold voltage setting resistor R1 and the second threshold voltage setting resistor R2, one end of the second threshold voltage setting resistor R2 is grounded, the other end of the second threshold voltage setting resistor R2 is connected to the polarity end of the first DC magnetic modulation coil excitation winding W1, the output end of the comparator is connected to the non-polarity end of the second DC magnetic modulation coil excitation winding W2, the polarity end of the second DC magnetic modulation coil excitation winding W2 is connected to one end of the second excitation current sampling resistor R4, the other end of the second excitation current sampling resistor R4 is grounded, the output end of the comparator is simultaneously connected to the input end of the low-pass filter, the non-polarity end of the intermediate frequency AC coil detection winding W3 is connected to the band-pass filter, and the non-polarity end of the high frequency AC coil detection winding W4 is connected to the high-pass filter;

[0068] The output voltage signal of the low-pass filter is added to the output voltage of the band-pass filter and connected to the front end of the intermediate frequency signal amplifier; the front end of the high-frequency signal amplifier is connected to the voltage output end of the high-pass filter, the output voltage signal of the tail end is added to the output voltage of the high-frequency signal amplifier and connected to the front end of the power amplifier, and the tail end of the power amplifier is connected to the secondary winding W s Polarity end connection, load resistance and secondary winding W s Non-polar end connection.

[0069] Optionally, the self-excited oscillation circuit is in different working states, and the comparator output alternately changes between two limit levels ±U with time.s , assuming that the initial comparator positive input voltage U p >Comparator negative input voltage U n At this time, the comparator outputs the forward limit voltage U s , and U p =U s *R1 / (R1+R2), comparator output voltage U s Acting on the nonlinear inductance L1 of the first DC magnetic modulation coil exciting winding W1, the excitation current I in the nonlinear inductance L1 ex1 Starting from zero, the voltage U on the excitation current sampling resistor R3 in the same circuit increases. n will also increase when its voltage increases to U n >U p When the comparator output turns to the negative limit voltage -U s , and U p =﹣U s *R1 / (R1+R2), -U s Acting on the nonlinear inductance L1 of the excitation winding W1, the excitation current I ex1 The voltage U on the first excitation current sampling resistor R3 in the same circuit decreases to a negative value. n It will also decrease to a negative value when its voltage increases to U n p When the comparator outputs the forward limit voltage U s Due to the symmetry of the excitation performance of the core T1, the comparator will continuously output a forward voltage U at fixed periods t1 and t2. s and forward voltage -U s , that is, the period is t1+t2 and the amplitude is U s square wave signal.

[0070] Optionally, the self-excited oscillation circuit, when the primary winding W p When a DC current flows through the core, the symmetry of the core excitation performance is destroyed, resulting in a bias proportional to the DC current, which causes the comparator to output a forward limit voltage U s And negative limit voltage ﹣U s The time of inconsistency t1≠t2, and the degree of inconsistency Δt is proportional to the DC flowing in the primary winding;

[0071] The comparator outputs a square wave signal to excite the two reversely connected first DC magnetic modulation coils T1 and second DC magnetic modulation coils T2, so that the same excitation generates magnetic fluxes in the first DC magnetic modulation coils T1 and second DC magnetic modulation coils T2 with equal magnitude and opposite directions, thereby canceling each other out;

[0072] ​The low-pass filter filters the high-frequency signal of the square wave voltage signal output by the comparator and directly converts it into a corresponding DC voltage signal;

[0073] The bandpass filter filters the low-frequency and high-frequency parts of the AC voltage signal induced in the intermediate frequency AC coil detection winding W3, and amplifies and outputs the intermediate frequency AC voltage small signal and the DC voltage small signal through the intermediate frequency amplifier;

[0074] The high-pass filter filters the low-frequency part of the AC voltage signal induced in the high-frequency AC coil detection winding W4, and then amplifies the high-frequency AC voltage small signal through the high-frequency amplifier for output.

[0075] Optionally, the power amplifier further amplifies the voltage signal to drive the secondary winding and the load resistor to output a secondary current;

[0076] The load resistor converts the current signal into a voltage signal;

[0077] The second DC magnetic modulation coil excitation winding W s When ripple current appears in the high-frequency AC coil T4, its ripple magnetic flux will generate an induced potential on the high-frequency AC coil detection winding W4 of the high-frequency induction coil, and drive the high-frequency signal amplifier and the power amplifier to generate an anti-phase current in the secondary winding to offset the ripple and high-frequency harmonics until the ripple magnetic flux induced in the high-frequency AC coil T4 is zero.

[0078] refer to Figure 1 As shown, Figure 1 The schematic diagram of a low-ripple zero-flux current transformer with a four-core five-winding structure is given. The zero-flux current transformer consists of two DC magnetic modulation coils, a medium-frequency AC coil, a high-frequency compensation coil and a circuit module. The DC magnetic modulation coil T1 consists of an excitation winding W1, a secondary winding W s , iron core C1, DC magnetic modulation coil T2 consists of excitation winding W2, secondary winding W s , iron core C2, the medium frequency AC coil T3 consists of the detection winding W3, the iron core C3 and the secondary winding W s The high-frequency AC coil T4 consists of the detection winding W4, the iron core C4 and the secondary winding W s The circuit module consists of a self-excited oscillator, a low-pass filter, a band-pass filter, a high-pass filter, an intermediate frequency signal amplifier, a high-frequency signal amplifier, a power amplifier, and a load resistor. The self-excited oscillator consists of threshold voltage setting resistors R1 and R2, excitation current sampling resistors R3 and R4, and a comparator. The iron core C1 and the excitation winding W1 constitute a nonlinear inductor L1, the iron core C2 and the excitation winding W2 constitute a nonlinear inductor L2, and the self-excited oscillator and the nonlinear inductors L1 and L2 constitute a self-excited oscillation circuit.

[0079] like Figure 2 As shown, the excitation winding W1 of the DC magnetic modulation coil T1 is evenly wound on the outer wall of the iron core C1, and the excitation winding W2 of the DC magnetic modulation coil T2 is evenly wound on the outer wall of the iron core C2. After the two coils are wound, their sizes are basically the same and they can be stacked up and down. The detection winding W3 of the medium frequency AC coil T3 is evenly wound on the outer wall of the iron core C3. After the coil is wound, it is placed on the outside of the DC magnetic modulation coil, so as to play the role of magnetic shielding of the DC magnetic modulation coil. The detection winding W4 of the high frequency AC coil T4 is evenly wound on the outer wall of the iron core C4. After the coil is wound, it is placed on the inside of the DC magnetic modulation coil, so as to play the role of magnetic shielding of the DC magnetic modulation coil. The four coils are arranged in accordance with Figure 2 After being placed in relative positions, the secondary winding is evenly wound on its outer side to form a whole zero flux current transformer coil.

[0080] When the primary winding W p When there are AC and DC currents in the circuit, the oscillator excites two reversely connected DC magnetic modulation coils T1 and T2 by outputting square waves, triangle waves or sinusoidal signals, and the odd harmonic components in the voltage signals induced on W1 and W2 cancel each other out, while the even harmonic components add up. The demodulator converts the even harmonic components into DC signals for output;

[0081] like Figure 1 As shown in the figure, the self-excited oscillation circuit is in different working states, and the comparator will output two limit levels ±U that change alternately over time. s , assuming that the initial comparator input voltage U p >U n At this time, the comparator outputs the forward limit voltage U s , and U p =U s *R1 / (R1+R2), U s Acting on the nonlinear inductance L1 of the excitation winding W1, the excitation current I in L1 ex1 Starting from zero, the voltage U on the excitation current sampling resistor R3 in the same circuit increases. n will also increase. When the current increases to the flip current I th , so that U n >U p When the comparator output turns to the negative limit voltage -U s , and U p =﹣U s *R1 / (R1+R2), -U s Acting on the nonlinear inductance L1 of the excitation winding W1, the excitation current I ex1 The voltage U on the excitation current sampling resistor R3 in the same circuit decreases to a negative value. nIt will also decrease to a negative value when the current decreases to the inversion current -I th , such that U n < U p When this occurs, the comparator will output the positive limit voltage U s . Due to the symmetry of the excitation performance of the iron core T1, as Figure 3 shown, when I dc is zero, I ex1 oscillates back and forth around point O from the inversion current I th to -I th . The comparator will continuously output the positive voltage U s and the positive voltage -U s with fixed periods t1 and t2, that is, a square wave signal with a period of t1 + t2 and an amplitude of U s .

[0082] When a direct current flows through the primary winding W p , the symmetry of the excitation performance of the iron core is destroyed, and a bias proportional to the direct current will be generated, that is, I dc > 0. Then the iron core is excited and induced with (I dc , B dc ) as the center. Due to the asymmetry and non-linearity of the iron core operating point, the time for the comparator to output the positive limit voltage U s and the negative limit voltage -U s is inconsistent, t1 < t2, and the degree of inconsistency Δt = t1 - t2 is proportional to the direct current flowing through the primary winding. The connected low-pass filter filters the high-frequency signal of the square wave voltage signal output by the comparator, thus directly converting it into a corresponding direct current voltage signal;

[0083] The intermediate-frequency AC winding T3 will induce an AC signal, which is added to the DC signal and then output to the intermediate-frequency signal amplifier. Due to the function of the band-pass filter and the frequency gain characteristics of this amplifier, it can mainly amplify the DC to intermediate-frequency signals and attenuate the high-frequency signals; the high-frequency AC winding T4, due to the function of the high-pass filter and the frequency gain characteristics of this amplifier, mainly amplifies the high-frequency signals and attenuates the intermediate and low-frequency signals; the high-frequency AC signal output by it is added to the DC intermediate-frequency signal output by the intermediate-frequency signal amplifier and then output to the power amplifier to drive the secondary winding W s to generate a secondary AC and DC current signal proportional to the primary winding W p , finally bringing the current transformer to the zero-flux state of negative feedback. The secondary current flowing through the load resistor generates the secondary voltage signal.

[0084] According to another aspect of the present invention, there is also provided a method for eliminating ripple according to a zero-flux current transformer, including:

[0085] By adding high-frequency coils and negative feedback circuits to offset the ripple and high-frequency interference generated by the system, when the secondary winding W s When there is ripple current I r , according to Ampere's circuit law:

[0086]

[0087] Among them, H r is the magnetic field strength of the core C4, N2 is the number of turns of the secondary winding, and l is the average magnetic path length of the core C4;

[0088] According to the magnetic properties of the iron core, there are:

[0089] B=μH r (2)

[0090] Wherein, μ is the magnetic permeability of the core C4;

[0091] Φ=BS (3)

[0092] Wherein, S is the cross section of the core C4;

[0093] According to the law of electromagnetic induction, the ripple magnetic flux φ generates an induced potential U on the detection winding W4 of the high-frequency induction coil. r , and drives the high-frequency signal amplifier and the power amplifier to generate the reverse ripple current I in the secondary winding r ', to offset the ripple current I r , until the ripple flux induced in coil T4 is zero, that is,

[0094] I r =I r ' (4).

[0095] The method of reducing the ripple of the zero flux current transformer is mainly to add high-frequency coils and negative feedback circuits to offset the ripple and high-frequency interference generated by the system. s When there is ripple current I r , according to Ampere's circuit law:

[0096]

[0097] Among them, N2 is the number of turns of the secondary winding, and l is the average magnetic path length of the core C4.

[0098] According to the magnetic properties of the iron core, there are:

[0099] B=μH r (2)

[0100] Wherein, μ is the magnetic permeability of the core C4.

[0101] Φ=BS (3)

[0102] Wherein, S is the cross section of the core C4.

[0103] According to the law of electromagnetic induction, the ripple magnetic flux φ will generate an induced potential U on the detection winding W4 of the high-frequency induction coil. r , and drives the high-frequency signal amplifier and the power amplifier to generate the reverse ripple current I in the secondary winding r ', to offset the ripple current I r , until the ripple flux induced in coil T4 is zero, that is,

[0104] I r =I r ' (4)

[0105] Therefore, when the zero flux current transformer adopts phase-sensitive demodulation, the system ripple is mainly modulation ripple; when the zero flux current transformer adopts peak difference demodulation, the system ripple includes inductive ripple and modulation ripple. Regardless of the sampling excitation demodulation method, a complex crystal oscillator excitation and demodulation circuit is required. At the same time, the existing zero flux transformer generally adopts a three-core four-winding structure. The inductive ripple and modulation ripple are amplified by the signal amplifier and the power amplifier and output to the secondary winding, and cannot be simply eliminated by the filtering circuit, because when there is a high-frequency signal in the primary, the secondary cannot normally respond to the waveform of the primary signal after filtering. The self-excited oscillation circuit does not allow the crystal oscillator to generate high-frequency signal oscillation excitation. At the same time, its demodulation circuit is a simple low-pass filter circuit that is easy to implement. At the same time, a high-frequency induction coil T4 is added. Through negative feedback and zero flux principles, the secondary can accurately sense the primary high-frequency signal, and at the same time greatly offset the ripple signal generated inside the system, so as to achieve the effect of significantly reducing the system ripple interference.

[0106] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0107] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0108] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0109] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0110] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0111] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A self-excited oscillation zero-flux current transformer, characterized in that: include: The zero flux current transformer comprises a first DC magnetic modulation coil T1, a second DC magnetic modulation coil T2, a medium frequency AC coil T3, the high frequency AC coil T4 and a circuit module; The first DC magnetic modulation coil T1 includes a first DC magnetic modulation coil core C1, a first DC magnetic modulation coil excitation winding W1 and a first secondary winding W s The second DC magnetic modulation coil core T2 includes a second DC magnetic modulation coil core C2, a second DC magnetic modulation coil excitation winding W2 and a second secondary winding W s ; The first DC magnetic modulation coil excitation winding W1 and the second DC magnetic modulation coil excitation winding W2 have the same number of turns and are evenly and densely wound on the circumference of the first DC magnetic modulation coil core C1 and the second DC magnetic modulation coil core C2 respectively.

2. The zero flux current transformer according to claim 1, characterized in that: The intermediate frequency AC coil T3 includes an intermediate frequency AC coil core C3, an intermediate frequency AC coil detection winding W3 and a third section secondary winding W s ; The medium frequency AC coil detection winding W3 is evenly and densely wound on the circumference of the medium frequency AC coil core C3; The intermediate frequency AC winding core C3 surrounds the first DC magnetic modulation winding core C1 and the second DC magnetic modulation winding core C2. In addition to serving as an intermediate frequency signal sensing core, the intermediate frequency AC winding core C3 also serves as a magnetic shield for the first DC magnetic modulation winding core C1 and the second DC magnetic modulation winding core C2.

3. The zero flux current transformer according to claim 2, characterized in that: The high-frequency AC coil T4 includes a high-frequency AC coil core C4, a high-frequency AC coil detection winding W4 and a fourth secondary winding W s ; The high-frequency AC coil detection winding W4 is evenly and densely wound on the circumference of the high-frequency AC coil core C4; The intermediate frequency AC coil core C3 surrounds the high frequency AC coil core C4 and serves as a magnetic shield for the high frequency AC coil core C4 in addition to being a intermediate frequency signal sensing core.

4. The zero flux current transformer according to claim 3, characterized in that: The zero flux current transformer also includes a primary winding W p , primary winding W p It is a turn of through-core conductor, passing through the central apertures of the first DC magnetic modulation coil T1, the second DC magnetic modulation coil T2, the medium frequency AC coil T3 and the high frequency compensation coil T4; Secondary winding W s It is evenly and densely wound on the circumference of the whole coil package composed of the first DC magnetic modulation coil package T1, the second DC magnetic modulation coil package T2, the medium frequency AC coil package T3 and the high frequency compensation coil package T4.

5. The zero flux current transformer according to claim 1, characterized in that: The circuit module includes a self-excited oscillator, a low-pass filter, a band-pass filter, a high-pass filter, an intermediate frequency signal amplifier, a high-frequency signal amplifier, a power amplifier and a load resistor; The self-excited oscillator includes a first threshold voltage setting resistor R1, a second threshold voltage setting resistor R2, a first excitation current sampling resistor R3, a second excitation current sampling resistor R4, and a comparator.

6. The zero flux current transformer according to claim 5, characterized in that: The first DC magnetic modulation coil core C1 and the first DC magnetic modulation coil excitation winding W1 constitute a nonlinear inductor L1, the second DC magnetic modulation coil core C2 and the second DC magnetic modulation coil excitation winding W2 constitute a nonlinear inductor L2, and the self-excited oscillator and the nonlinear inductors L1 and L2 constitute a self-excited oscillation circuit.

7. The zero flux current transformer according to claim 6, characterized in that: The negative input end of the comparator is respectively connected to the first excitation current sampling resistor R3 and the non-polar end of the first DC magnetic modulation coil excitation winding W1, the other end of the first excitation current sampling resistor R3 is grounded, the positive input end of the comparator is respectively connected to one end of the first threshold voltage setting resistor R1 and the second threshold voltage setting resistor R2, one end of the second threshold voltage setting resistor R2 is grounded, the other end of the second threshold voltage setting resistor R2 is connected to the polarity end of the first DC magnetic modulation coil excitation winding W1, the output end of the comparator is connected to the non-polarity end of the second DC magnetic modulation coil excitation winding W2, the polarity end of the second DC magnetic modulation coil excitation winding W2 is connected to one end of the second excitation current sampling resistor R4, the other end of the second excitation current sampling resistor R4 is grounded, the output end of the comparator is simultaneously connected to the input end of the low-pass filter, the non-polarity end of the intermediate frequency AC coil detection winding W3 is connected to the band-pass filter, and the non-polarity end of the high frequency AC coil detection winding W4 is connected to the high-pass filter; The output voltage signal of the low-pass filter is added to the output voltage of the band-pass filter and connected to the front end of the intermediate frequency signal amplifier; the front end of the high-frequency signal amplifier is connected to the voltage output end of the high-pass filter, the output voltage signal of the tail end is added to the output voltage of the high-frequency signal amplifier and connected to the front end of the power amplifier, and the tail end of the power amplifier is connected to the secondary winding W s Polarity end connection, load resistance and secondary winding W s Non-polar end connection.

8. The zero flux current transformer according to claim 5, characterized in that: The self-excited oscillation circuit is in different working states, and the comparator output changes alternately between two limit levels ±U s , assuming that the initial comparator positive input voltage U p >Comparator negative input voltage U n At this time, the comparator outputs the forward limit voltage U s , and U p =U s *R1 / (R1+R2), comparator output voltage U s Acting on the nonlinear inductance L1 of the first DC magnetic modulation coil exciting winding W1, the excitation current I in the nonlinear inductance L1 ex1 Starting from zero, the voltage U on the excitation current sampling resistor R3 in the same circuit increases. n will also increase when its voltage increases to U n >U p When the comparator output turns to the negative limit voltage -U s , and U p =﹣U s *R1 / (R1+R2), -U s Acting on the nonlinear inductance L1 of the excitation winding W1, the excitation current I ex1 The voltage U on the first excitation current sampling resistor R3 in the same circuit decreases to a negative value. n It will also decrease to a negative value when its voltage increases to U n p When the comparator outputs the forward limit voltage U s Due to the symmetry of the excitation performance of the core T1, the comparator will continuously output a forward voltage U at fixed periods t1 and t2. s and forward voltage -U s , that is, the period is t1+t2 and the amplitude is U s square wave signal.​ 9. The zero flux current transformer according to claim 8, characterized in that: The self-excited oscillation circuit, when the primary winding W p When a DC current flows through the core, the symmetry of the core excitation performance is destroyed, resulting in a bias proportional to the DC current, which causes the comparator to output a forward limit voltage U s And negative limit voltage ﹣U s The time of inconsistency t1≠t2, and the degree of inconsistency Δt is proportional to the DC flowing in the primary winding; The comparator outputs a square wave signal to excite the two reversely connected first DC magnetic modulation coils T1 and second DC magnetic modulation coils T2, so that the same excitation generates magnetic fluxes in the first DC magnetic modulation coils T1 and second DC magnetic modulation coils T2 with equal magnitude and opposite directions, thereby canceling each other out. The low-pass filter filters the high-frequency signal of the square wave voltage signal output by the comparator and directly converts it into a corresponding DC voltage signal; The bandpass filter filters the low-frequency and high-frequency parts of the AC voltage signal induced in the intermediate frequency AC coil detection winding W3, and amplifies and outputs the intermediate frequency AC voltage small signal and the DC voltage small signal through the intermediate frequency amplifier; The high-pass filter filters the low-frequency part of the AC voltage signal induced in the high-frequency AC coil detection winding W4, and then amplifies the high-frequency AC voltage small signal through the high-frequency amplifier for output.

10. The zero flux current transformer according to claim 9, characterized in that: The power amplifier further amplifies the voltage signal to drive the secondary winding and the load resistor to output a secondary current; The load resistor converts the current signal into a voltage signal; The second DC magnetic modulation coil excitation winding W s When ripple current appears in the high-frequency AC coil T4, its ripple magnetic flux will generate an induced potential on the high-frequency AC coil detection winding W4 of the high-frequency induction coil, and drive the high-frequency signal amplifier and the power amplifier to generate an anti-phase current in the secondary winding to offset the ripple and high-frequency harmonics until the ripple magnetic flux induced in the high-frequency AC coil T4 is zero.

11. A method for eliminating ripples in a zero-flux current transformer according to claim 1, characterized in that: include: By adding high-frequency coils and negative feedback circuits to offset the ripple and high-frequency interference generated by the system, when the secondary winding W s When there is ripple current I r , according to Ampere's circuit law: Among them, H r is the magnetic field strength of the core C4, N2 is the number of turns of the secondary winding, and l is the average magnetic path length of the core C4; According to the magnetic properties of the iron core, there are: B=μH r (2) Wherein, μ is the magnetic permeability of the core C4; Φ=BS (3) Wherein, S is the cross section of the core C4; According to the law of electromagnetic induction, the ripple magnetic flux φ generates an induced potential U on the detection winding W4 of the high-frequency induction coil. r , and drives the high-frequency signal amplifier and the power amplifier to generate the reverse ripple current I in the secondary winding r ', to offset the ripple current I r , until the ripple flux induced in coil T4 is zero, that is, I r =I r ' (4)。

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