44 results about "Compensation winding" patented technology

The application relates to an axial-radial hybrid excitation magnetic bearing with a compensation winding, characterized in that the axial-radial hybrid excitation magnetic bearing comprises a rotor, an axial stator, a sleeve, a radial stator, a radial stator magnetic yoke, an axial control winding, a radial control winding, a permanent magnet ring and a compensation winding; the radial stator is arranged on the outer circumferential side of the rotor and comprises a plurality of radial stator iron core magnetic poles uniformly distributed in the circumferential direction and having the radial control winding wound thereon; two axial stators are symmetrically arranged on the upper and lower sides of the circumferential part of the rotor and the radial stator and the outer circumferential parts of the two axial stators are connected with the sleeve; the radial stator magnetic yoke is arranged on the outer circumferential side of the radial stator, and two permanent magnet rings are respectively arranged between the two axial stators and the radial stator magnetic yoke; the axial control winding is wound between the sleeve and the radial stator magnetic yoke; and two compensation windings are respectively arranged between the axial stators and the permanent magnet rings. The axial-radial hybrid excitation magnetic bearing has the advantages of compact axial and radial design, low power consumption, small volume, adjustable rigidity, inhibition of axial eddy current effect and high stability.

The application relates to a natural ester transformer winding structure, comprising a winding wire cake, further comprising: a shielding section arranged at the head end of the winding wire cake; and a large oil channel arranged at the head end and the tail end of the winding, the thickness of the large oil channel being larger than that of a basic oil channel in the winding. The above scheme provided by the application increases the longitudinal capacitance of the winding, the longitudinal capacitance can compensate the ground capacitance current of the winding, the impulse voltage distribution of the winding is more uniform, the impulse overvoltage capacity of the transformer is higher, if the shielding section is not used, the impulse voltage mostly falls on the head end of the winding, which is very harmful to the insulation of the head end of the winding, meanwhile, the arrangement of the large oil channel reduces the hot spot temperature rise of the winding end, improves the average temperature rise of the whole winding, ensures that the temperature rise of the transformer winding is more uniform, and further improves the reliability of the transformer during operation.

An EMI filter including a core forming a closed magnetic circuit, the core having first, second and third stems extending in parallel directions, the second stem being disposed between the first and third stems. The ends of the stem are connected by first and second bridge legs. A first coil, which is part of the first DC power line conductor, is disposed around the first stem and / or the first bridge leg. A second coil, which is part of a DC power line conductor, is disposed around the third stem and / or the second bridge leg. The compensation winding is arranged on the core and comprises a first compensation coil and a second compensation coil, the first compensation coil is arranged around the first core column and / or the first bridge leg, and the second compensation coil is arranged around the third core column and / or the second bridge leg for inducing a magnetic flux density in the second core column in the following direction. The direction is opposite to the direction of the magnetic flux density generated in the second stem by the direct current supplied through the first coil and through the second coil for reducing the resulting magnetic flux in the second stem.

The application discloses a kind of anti DC bias magnetic methods and current transformers based on magnetic permeability feedback compensation, comprising: the magnetic permeability of current transformer core is acquired in real time by magnetic permeability measuring unit;According to the relationship model of magnetic permeability and DC component established in advance, the DC component of invading current transformer is determined based on the magnetic permeability acquired;DC bias compensation unit generates reverse DC counter-biasing according to the DC component determined on compensation winding.The application realizes real-time monitoring and dynamic compensation adjustment to the magnetization state of transformer core by introducing magnetic permeability measuring unit and magnetic permeability feedback control, compared with traditional open-loop compensation or simple current feedback, can more accurately judge the saturation degree of magnetic core, adjusts compensation strategy in time according to the change of magnetic core state, effectively avoids compensation lag or overcompensation problem, improves the adaptability and measurement stability of transformer in complex current environment.

The utility model provides a two-stage separation type current transformer with an air gap. The two-stage separation type current transformer with the air gap comprises a first iron core, a second iron core, a primary winding, a secondary winding and a compensation winding. The first iron core and the second iron core are both provided with air gaps, and the magnetic conductivity of the first iron core is smaller than that of the second iron core; the primary winding is wound on one side of the first iron core and one side of the second iron core, the secondary winding is wound on the other side of the first iron core and the other side of the second iron core, and the compensation winding and the secondary winding are connected in parallel; the primary winding, the first iron core and the secondary winding form a first-stage current transformer, and the primary winding, the second iron core, the secondary winding and the compensation winding form a second-stage current transformer. The first iron core is an auxiliary iron core and bears the main magnetic flux and the induced electromotive force of the secondary circuit, the magnetic induction intensity is high, and the exciting current is large. The error of the current transformer can be compensated through the compensation current, and the accuracy of the current transformer is improved.

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

The invention relates to a multiplexing leakage inductor injection voltage compensation type doubly-fed active EMI filtering device. The device comprises a feed-forward compensation module, a feedback compensation module and a compensation winding module. The output end of the feed-forward compensation module is connected with the first end of the compensation winding module; the output end of the feedback compensation module is connected with the second end of the compensation winding module, and the compensation winding module is connected with the coupling inductor; the feed-forward compensation module is used for detecting a common-mode voltage and generating a first compensation voltage according to the common-mode voltage; the compensation winding module is used for coupling the first compensation voltage to the coupling inductor so as to carry out feed-forward compensation on the common-mode voltage; the feedback compensation module is used for detecting the common-mode voltage after feedforward compensation and generating a second compensation voltage according to the common-mode voltage after feedforward compensation; the compensation winding module is also used for coupling the second compensation voltage to the coupling inductor so as to perform feedback compensation on the common-mode voltage after feedforward compensation; in this way, EMI suppression is achieved.

The invention relates to the technical field of power electronics, and discloses a self-adaptive harmonic isolation method and device based on dynamic regulation and control of magnetic flux of a transformer, and the method comprises the steps: calculating the total harmonic distortion rate of a power grid to analyze the harmonic pollution level of the power grid, and calculating the harmonic distortion rate of the power grid according to the harmonic pollution level; generating a target magnetic flux compensation instruction for suppressing the dominant subharmonic corresponding to the power grid; inputting the target magnetic flux compensation instruction into a power converter connected with an auxiliary compensation winding in a preset harmonic isolation transformer to generate compensation harmonic magnetic flux of the target magnetic flux compensation instruction; the compensation harmonic magnetic flux is injected into the transformer iron core, the dominant sub-harmonics are offset, offset net magnetic flux is obtained, and a target magnetic flux compensation instruction and a magnetic flux error of the offset net magnetic flux are calculated; and when the magnetic flux error accords with a preset magnetic flux error threshold value, sine wave back electromotive force is generated in a main winding in the harmonic isolation transformer by utilizing the offset net magnetic flux so as to execute harmonic isolation. The isolation effect of harmonic propagation can be improved.

The invention relates to a current sensing circuit. The current sensing circuit comprises a magnetic ring module, a primary winding, a current detection module, a ripple suppression module and a compensation module. The primary winding is wound on the magnetic ring module and is connected with a current to be measured; the current detection module comprises a current detection winding and a current detection circuit, and the current detection winding is wound on the magnetic ring module; the current detection circuit is driven by the power supply voltage to generate square wave excitation voltage; the ripple suppression module comprises a suppression winding and a ripple suppression circuit; the suppression winding is wound on the magnetic ring module; the suppression circuit excites the magnetic ring module to generate target magnetic flux through the suppression winding under the action of the square wave excitation voltage so as to suppress ripple current in the current to be detected; the compensation module comprises a compensation winding and a compensation circuit; the compensation winding is wound on the magnetic ring module; the compensation circuit is connected with the current detection circuit and the ripple suppression circuit and outputs feedback current to the compensation winding, so that the compensation winding generates compensation magnetic flux in the magnetic ring module, and the magnetic ring module is in a target magnetic flux state.

The invention provides a zero-flux implementation system and method for a current transformer for high-voltage power transmission, and the system comprises an iron core, a primary winding, a detection winding, a compensation winding, a Hall sensor group, a signal processing unit, and a zero-flux control unit. Detecting an initial low-frequency magnetic flux signal and an initial high-frequency magnetic flux signal of the iron core; the signal processing unit is used for processing the collected initial low-frequency magnetic flux signal and the initial high-frequency magnetic flux signal, dynamically allocating weights according to frequency characteristics of the processed signals, and then performing fusion processing to generate a fused magnetic flux detection signal; and the zero magnetic flux control unit is used for inputting the magnetic flux detection signal as an error signal and adjusting the compensation current of the compensation winding by adopting a control algorithm. According to the system and the method, the limitation of a traditional single detection mode is successfully solved through a fusion detection technology and dynamic distribution of signal weights.

The invention discloses an impedance self-adaptive matching device based on a secondary side double-winding transformer and a control method, and relates to the technical field of transformer impedance self-adaptive matching. The device comprises a transformer, a tap selector, a switching unit, a monitoring unit and a control unit. The secondary side of the transformer is provided with a main winding and a compensation winding, the head end of the main winding is connected with a load, the tail end of the main winding and the tail end of the compensation winding are grounded, a tap of the tap selector is connected with a compensation winding turn, the switching unit is connected with the tap, the load and the control unit, and the monitoring unit is connected with the control unit and the load. According to the control method, load current, voltage and phase difference are acquired through the monitoring unit, the control unit calculates the optimal impedance ratio and target impedance, the number of connected turns of the compensation winding is determined, and the switching unit is controlled to adjust the number of turns and circulate. The invention can adapt to the load power factor change in real time, improve the impedance matching speed to 50ms level, reduce the loss, and is compatible with the transformation of the existing transformer, and the transformation cost is low.

The invention discloses a method and a device for suppressing common-mode interference voltage, a power supply circuit, a storage medium and a computer program product, the method is applied to the design of the power supply circuit integrated by a PFC module and a switching power supply module for suppressing the common-mode interference voltage, and a primary winding of a transformer of the switching power supply module is used as a PFC inductor of the PFC module. A switching tube of the PFC module is used as a switching tube in the switching power supply module; the method comprises the following steps: determining parameters of a compensation winding after determining a winding of the transformer; and according to the parameters of the compensation winding, winding a winding wire of the compensation winding into a magnetic circuit of a magnetic element of the power supply circuit so as to compensate a common-mode voltage generated in the power supply circuit by using an equivalent voltage generated by the compensation winding to suppress common-mode interference. According to the scheme, the compensation winding is additionally arranged on the magnetic circuit of the power supply circuit obtained by integrating the PFC module and the switching power supply module, common-mode voltage generated in the power supply circuit is compensated, common-mode interference is suppressed, and the cost is low.

The application provides a stator structure and a motor structure with the same, wherein the stator structure comprises: a plurality of stator modules arranged in a splicing mode, each of the stator modules comprising a basic winding structure, a first compensation winding structure arranged at a first side of the basic winding structure, the first compensation winding structure comprising a plurality of second coils arranged in an array, and a second compensation winding structure arranged at a second side of the basic winding structure, the second compensation winding structure comprising a plurality of third coils arranged in an array, the first side and the second side of the basic winding structure being two sides arranged oppositely in a first direction; and wherein the first compensation winding structure of one of the two stator modules arranged adjacently in the first direction is arranged in a lap joint mode with the second compensation winding structure of the other stator module. The technical scheme of the application can effectively solve the problem of unstable movement of a mover structure at a splicing gap between adjacent stator modules in the related art.

The invention discloses a voltage and current integrated sensor and a three-phase measurement system and method, and relates to the technical field of electric power measurement, and the system comprises a current measurement module which comprises a magnetic core used for generating magnetic flux after a primary current passes through a primary side conductor, and a secondary side winding used for collecting a magnetic core induction signal, the compensation winding is used for carrying out fixed transformation ratio output on the magnetic core induction signal according to the selected measuring range; the voltage measuring module comprises a puncture unit used for collecting voltage in a puncture needle sampling mode, a voltage dividing network used for selecting the voltage dividing ratio according to the voltage amplitude and outputting the voltage after voltage dividing, and a buffer amplifier used for amplifying the voltage after voltage dividing. And the signal conditioning module is used for carrying out standardized conditioning output on the current and the voltage output by the current measurement module and the voltage measurement module so as to carry out power load identification. High-quality analog signals can be provided for rear-end digital equipment, and the requirements of power load identification and electric energy quality analysis are met.

The invention, which belongs to the converter field, discloses a controllable current converter comprising a processor, a digital adjusting module, a voltage sampling resistor, a voltage conversion resistor, a first current transformer and a second current transformer. The processor is electrically connected with the digital adjusting module through the communication control end; the voltage sampling resistor is connected in series between secondary windings of the first current transformer; the voltage conversion resistor is connected in series between the secondary winding and the compensation winding of the first current transformer; the secondary winding and the compensation winding of the first current transformer are respectively connected with the output of the second current transformer in parallel; the primary head end of the second current transformer is connected with the digital adjusting module, and the primary tail end is connected with the common terminal potential. The processor is used for calculating an amplitude adjusting quantity and a phase adjusting quantity; and the digital adjusting module is used for controlling the amplitude of the output current and the phase of the output current according to the amplitude adjusting quantity and the phase adjusting quantity. Therefore, through the processor and the digital adjusting module, the problem that the accuracy of the current converter is not high can be solved.

Techniques are disclosed relating to sensing an object using an inductive proximity sensor. In an embodiment, an apparatus includes a transmission coil having turns formed on a first circuit board and including a first primary winding having a first winding direction. The apparatus further includes a first sensor coil having turns formed on a second circuit board and including a second primary winding having a second winding direction and a second sensor coil having turns formed on a third circuit board and including a third primary winding having a third winding direction opposite to the second winding direction. The coils are spaced apart from one another in a common axial direction and at least one of the coils includes a compensation winding having at least one turn, where the compensation winding is arranged radially outside of, and has a winding direction opposite to, the same coil's primary winding.

The invention discloses a flexible Rogowski coil current sensor and a measuring method. The sensor comprises a shell, a main coil and a connector module, and is characterized in that an I-shaped framework cylinder with a compensation winding is arranged in the shell, and the framework cylinder is sleeved on the periphery of an interface gap formed by butt joint of a fixed end and a movable end of the main coil. The compensation winding and the main winding are connected in series and then are connected to the integral circuit, additional electromotive force is generated through residual magnetic flux at the induction gap, and signal loss caused by discontinuous structures is compensated. The measurement method comprises the steps of determining compensation parameters, arranging a compensation winding, performing electrical connection and establishing a mathematical model through self-calibration to calibrate output. Through combination of structure compensation and algorithm calibration, measurement errors at the joint of the open type Rogowski coil are effectively eliminated, and the open type Rogowski coil has the advantages of being high in precision, compact in structure and high in adaptability.

The application relates to a current transformer and a metering device. The current transformer comprises an input winding, a proportional winding, a compensation winding, a first core and a second core; the input winding passes through the first core and the second core at the same time, the proportional winding is wound on the first core and the second core, the compensation winding is wound on the first core, and the proportional winding is electrically connected with the compensation winding; the physical characteristics of the first core are the same as those of the second core; the compensation winding is used for compensating corresponding excitation errors between the current provided by the input winding and the current actually output by the proportional winding; the first-order excitation error of the proportional winding is the same as the second-order excitation error of the compensation winding, and the error of the current transformer is the product between the first-order excitation error and the second-order excitation error. The metering device comprises the current transformer.

The application discloses a low-harmonic strong-coupling permanent-magnet hollow compensation pulse generator, which comprises a stator and a rotor arranged in sequence from outside to inside, and the rotor comprises a cage rotor compensation assembly; the cage rotor compensation assembly comprises two sets of symmetrically distributed cage rotor compensation windings; each set of cage rotor compensation windings comprises a plurality of bars arranged in bar grooves of the rotor; the bars form a plurality of pole number structures, and adjacent pole number structures are arranged at intervals; the bars of each set of cage rotor compensation windings are connected in a mode from both sides to the middle or from the middle to both sides; two bars connected in each group are connected through end rings; and a starting end bar and an ending end bar are connected to form a closed loop. The cage rotor compensation assembly compensation structure specially designed in the application not only has the advantages of a solid squirrel cage structure, high mechanical strength and suitability for high-speed operation, but also has the advantages that a winding type winding can be flexibly designed according to pole pairs of the motor, and the rotor harmonics can be effectively controlled.

A control device (1) for operating a load (10) by means of a pulse width modulated voltage signal through a cable harness (20) comprising two or more control lines (21, 22, 23), comprising: a signal generator (30), a plurality of signal generators (21, 22, 23) for generating the pulse width modulated voltage signal and feeding the pulse width modulated voltage signal into a respective one of the control lines (21, 22, 23); a transformer (40), which has a winding (41, 42, 43) for each of the control lines (21, 22, 23) and a compensation winding (44); and a regulator circuit (50), which is designed to regulate the voltage applied on the compensation winding (44) in order to reduce possible common-mode voltages on the control lines (21, 22, 23). According to the invention, the regulator circuit (50) is designed to detect the currently applied voltages of the respective voltage signal on the control lines (21, 22, 23) between the transformer (40) and the load (10) and to average therefrom as a regulating variable for regulating the voltage applied on the compensation winding (44). Furthermore, the control device comprises a low-pass filter unit (60, 70), which is designed to supply a reference variable, which is obtained from a low-pass filtering of a signal, to the regulator circuit (50) in order to regulate the voltage applied to the compensation winding (44), the signal corresponds to a common mode voltage of a pulse width modulated voltage signal output by the signal generator (30) onto the control lines (21, 22, 23) or is provided by a microprocessor unit (80).

The invention relates to the technical field of magnetic variable measurement, and discloses a closed-loop fluxgate current detection system, which is characterized in that a self-excited oscillation unit is connected with a PAC conversion unit, the PAC conversion unit is connected with an integration unit, the duty ratio of a square wave signal is converted into a voltage deviation signal, and the voltage deviation signal is provided for the integration unit; the integration unit is connected with the feedback compensation unit and is used for integrating the voltage deviation signal and providing an integration voltage; the self-excited oscillation unit adopts a symmetrical driving structure comprising an analog switch, and provides a square wave signal representing a duty ratio for the PAC conversion unit; and the feedback compensation unit is connected with the compensation winding, outputs a voltage signal in proportion to the current to be detected and drives the compensation winding to generate a counteracting magnetic field so as to form closed-loop detection. The problems of low bandwidth, zero drift, structure limitation and high cost in the prior art are solved, and the purposes of high bandwidth, openable installation, low ripple output, high precision and extremely high symmetry and consistency are achieved.

This application provides a current sensor and electronic device based on multiple sampling windings. The current sensor includes a sensing module, a compensation module, and a processing module. A primary winding is wound on the main magnetic core and an auxiliary magnetic core. A secondary winding is wound on the main magnetic core and an auxiliary magnetic core, and is connected to the processing module. Multiple sampling windings are wound on the main magnetic core, and each sampling winding is connected to the input terminal of the compensation module. A compensation winding is wound on the auxiliary magnetic core and is connected to the output terminal of the compensation module. This application uses multiple sampling windings to solve the problem of errors in current detection caused by differences in magnetic induction intensity at different positions of the main magnetic core. Multiple sampling windings allow for accurate characterization of the excitation current of the primary winding, thereby improving the sampling accuracy of the current sensor. This application can more accurately detect changes in the amplitude and phase of the filtered induced electromotive force, while reducing the influence of noise and improving the anti-interference performance of the current sensor.

The present invention provides a device and method for suppressing the excitation frequency noise of a fluxgate current sensor, comprising a fluxgate structure having a primary winding passing through two circular magnetic cores and a secondary winding divided into first and second windings that generate excitation currents in opposite directions. A compensation winding is wound around the two circular magnetic cores and connected to a compensation power supply and a load resistor. A filtering and demodulation circuit filters the excitation currents of the first and second windings to obtain a measurement signal. A PI controller receives the measurement signal and outputs a feedback current to maintain zero flux. A signal acquisition and noise spectrum analysis module analyzes the noise spectrum of the output signal and controls the compensation power supply to output a compensation current. The compensation winding current is a superposition of the feedback current and the compensation current, and a voltage signal is output through the load resistor. The present invention solves the noise problem caused by the excitation current by adding a compensation winding and a magnetic core and analyzing the specific frequency noise in the output signal to control an external current source to apply a compensation current to the compensation winding.

Transformer arrangement for reactive power compensation in an AC electrical network, comprehensive - a magnetic core, - at least one primary winding and at least one secondary winding of the transformer, characterized by that at least one compensation winding is arranged on the magnetic core, which is not intended to supply an external electrical load, wherein the compensation winding together with at least one capacitive element forms a self-sufficient compensation circuit, and wherein the compensation winding is magnetically coupled to a transformer winding whose reactive power component is to be compensated, wherein the compensation current flowing in the compensation circuit is generated by electromagnetic processes in the magnetic circuit of the transformer.

The utility model discloses a distribution line isolation compensation device, which is connected between a system bus and a protection line to realize isolation and compensation of the protection line when a single-phase earth fault occurs, and comprises a primary winding, a load winding and a compensation winding which are mutually coupled, the primary winding is respectively connected with each phase of a system bus; the load winding is respectively connected with each phase of the protection circuit and supplies power to power distribution equipment of the protection circuit; the compensation winding and the load winding are opposite in polarity, and neutral points are grounded. According to the utility model, isolation of a protection circuit and compensation of the protection circuit when a single-phase earth fault occurs can be realized, rapid arc extinguishing is realized, efficiency is improved, occurrence of electric shock danger of personnel is avoided, system construction and maintenance cost is greatly reduced, and the system is suitable for popularization and application. Various faults caused by mutual cooperation among a plurality of devices are avoided, and reliable guarantee is provided for stable operation of the system.

The invention discloses a self-adaptive load elevator transformer system which comprises a three-phase iron core structure used for constructing a three-phase magnetic flux path; the magnetic flux compensation winding is used for generating compensation magnetic flux; the data acquisition unit is used for acquiring three-phase current, voltage, magnetic field and temperature signals; the algorithm processing unit is used for executing a self-adaptive load algorithm, a composite spectrum self-shaping power optimization algorithm and a self-balancing energy distribution algorithm inspired by thermodynamics; the compensation execution unit is used for generating compensation magnetic flux according to an algorithm result; the algorithm processing unit performs cross fusion on algorithms to form a unified multi-dimensional magnetic flux compensation model; and the compensation execution unit dynamically adjusts the tap position and the output characteristic of the transformer according to the output result of the fusion algorithm. The method has the following beneficial effects: deep fusion of algorithms is realized, and the problems of low efficiency, high no-load loss, slow dynamic response, hotspot management and the like in the traditional technology are solved.

The application provides a kind of fluxgate current sensor circuit, including excitation circuit, excitation winding L1, compensation winding L2, error amplifier circuit, low-pass filter circuit and sampling circuit, excitation winding L1 is connected between two bridge arms of excitation circuit for detecting excitation current, excitation current is fed back to compensation winding L2 after error amplifier circuit, low-pass filter circuit and sampling circuit in turn, by measuring the current flowing through compensation winding L2, the value of the measured current can be known. The application adopts a more optimal excitation self-oscillation scheme for detecting small current, with higher detection accuracy.

A transformer includes a primary winding, a secondary winding, an external capacitor, and a compensation winding. The primary winding has a first end and a second end, which are respectively connected to the first potential point and the second potential point of a primary side circuit. The secondary winding has a third end and a fourth end, which are respectively connected to the third potential point and the fourth potential point of a secondary side circuit. The compensation winding has a fifth end and a sixth end, wherein one is connected to the first potential point and the other is connected to the third potential point via the external capacitor. The compensation winding is arranged between the primary winding and the secondary winding. The potential induced by the compensation winding is equal to that induced by the secondary winding. Also, a power converter using the transformer is provided.

The application provides a current transformer with fixed primary turns and wide variable ratio, which is composed of two current transformers CT1, CT2 and a switching switch K1. The current transformer comprises a primary coil, a secondary proportional winding, an error current detection winding, a compensation winding and an operational amplifier. The current transformer of the application adopts a three-stage iron core, an active compensation design, the primary winding N1 of the current transformer CT1 adopts fixed turns, the primary winding N1' of the current transformer CT2 adopts a variable turns design, and the error current is fed back to the compensation winding through the detection winding on the iron core, so that the problem of excessive input impedance of small current can be solved, the proportional error under small current can be greatly reduced, and the current measurement accuracy is effectively improved.

An EMI filter (4) comprises a core (5) forming a closed magnetic circuit, the core (2) having a first core pillar (1), a second core pillar (2), and a third core pillar (3) extending in a parallel direction, with the second core pillar (2) positioned between the first core pillar (1) and the third core pillar (3). The ends of the core pillars (1, 2, 3) are connected by first bridging legs (6) and second bridging legs (7). A first coil (9), forming part of a first DC conductor (10), is arranged around the first core pillar (1) and / or the first bridging legs (6). A second coil (22), forming part of a first DC conductor (10), is arranged around the third core pillar (3) and / or the second bridging legs (7).A compensation winding (14) is arranged on the core (5) and comprises a first compensation coil (25) and a second compensation coil (26), wherein the first compensation coil is arranged around the first core pillar (1) and / or the first bridging legs (6) and the second compensation coil (26) is arranged around the third core pillar (3) and / or the second bridging legs (7), to induce a magnetic flux density (17) in the second core pillar (2) in a direction (18) opposite to the direction (19) of a magnetic flux density (20) generated in the second core pillar (2) by a direct current supplied through the first coil (9) and through the second coil (22), to reduce a resultant magnetic flux in the second core pillar (2).