DC Current Sensor Research Articles

High-efficiency module-integrated photovoltaic power conditioning system

A module-integrated, photovoltaic (PV) power conditioning system with a high-efficiency, high step-up DC–DC converter is proposed. The step-up DC–DC converter employs an active-clamp circuit for soft switching of the power semiconductor switches. Also, a dual series-resonant rectifier is employed in order to remove the reverse-recovery problem of the output-rectifying diodes and to provide a much higher voltage conversion ratio. The PV current is estimated without using a DC current sensor, and the PV current ripple reduction technique is suggested to reduce the current ripple without an external component. A 1 kW prototype for the PV voltage range of 30–60 V is implemented, and all algorithms and controllers are implemented on a single-chip microcontroller. Experimental results show that the power efficiency is 92.5–94% and the ripple current is 3.5% of the rated input current.

DC sensor based on magnetic potential self-balance and feedback compensation

A new type of DC current sensor for 10 000 A, which integrates the advantages of DC measurement devices based on the open-loop and closed-loop principle, is presented. One magnetic core carrying two windings is designed as a magnetic potential self-balance loop. In order to detect and compensate the remaining ampere-turns except magnetic potential self-balanced, two feedback compensation detection magnetic cores are designed as a feedback compensation loop. Its operation principle and characteristics, including stability, error analysis and dynamic response, are analysed in detail. Finally, its validity is verified by experiment and the results show that the measuring accuracy of the proposed DC sensor can be enhanced up to 0.13% whereas the accuracy of a conventional DC sensor is only 0.5%.

A SQUID series array dc current sensor

Superconducting quantum interference device (SQUID) sensors are used to sense changes invarious physical quantities, which can be transformed into changes in the magnetic fluxthreading the SQUID loop. We have developed a novel SQUID array dc current sensor. Thedevice is based on a series array of identical dc SQUIDs. An input signal current to bemeasured is coupled tightly but non-uniformly to the SQUID array elements. The inputsignal coupling to the individual array elements is chosen such that a single-valued,non-periodic overall voltage response is obtained. Flux offsets in the individual SQUIDswhich would compromise the sensor voltage response are avoided or can be compensated.We present simulations and experimental results on the SQUID Array for Dc(SQUAD) current sensor current sensor performance. A dc current resolution of<1 nA in a measurement bandwidth of 0–25 Hz is achieved for an input inductance ofLIn<3 nH.

Transformer-Based DC Current Sensor For Digitally Controlled Power Supplies

Twenty years ago, R. Severus presented a transformer-based circuit that is able to measure DC currents. However, this circuit did not experience a break-through in the industry or even academic world because it requires too many components and is unable to measure small currents. This paper enhances this circuit so that it becomes feasible to measure currents down to zero. The circuit complexity is no longer an obstacle because in digital controlled power supplies the DSP provides the required auxiliary functionalities. The feasibility of the proposed circuit has been proven by hardware experiment.

Highly Accurate Fiber-Optic DC Current Sensor for the Electrowinning Industry

A fiber-optic current sensor for direct currents up to 500 kA is presented. Applications include current measurement for process control and protection in the electrowinning industry, for example at aluminum smelters. The sensor offers significant advantages with regard to performance and ease of installation compared to state-of-the-art Hall-effect-based current transducers. The sensor exploits the Faraday effect in an optical fiber and measures the path integral of the magnetic field along a closed loop around the current-carrying bus bars. The differential magnetooptic phase shift of left and right circular light waves propagating in the fiber is detected by means of a novel polarization-rotated reflection interferometer. Fiber gyroscope technology is employed for signal detection and processing. The fiber is packaged in a flexible strip of fiber reinforced epoxy, which can be installed without opening the current-carrying bus bars. Subsequent recalibration is not necessary. The sensor achieves accuracy within plusmn0.1% over a wide range of currents and temperatures

Photovoltaic Power Conditioning System With Line Connection

A photovoltaic (PV) power conditioning system (PCS) with line connection is proposed. Using the power slope versus voltage of the PV array, the maximum power point tracking (MPPT) controller that produces a smooth transition to the maximum power point is proposed. The dc current of the PV array is estimated without using a dc current sensor. A current controller is suggested to provide power to the line with an almost-unity power factor that is derived using the feedback linearization concept. The disturbance of the line voltage is detected using a fast sensing technique. All control functions are implemented in software with a single-chip microcontroller. Experimental results obtained on a 2-kW prototype show high performance such as an almost-unity power factor, a power efficiency of 94%, and a total harmonic distortion (THD) of 3.6%

Upgrade Fe-50%Ni alloys for open-loop DC current sensor: Design and alloy-potential characteristics

This paper deals with the DC current sensor with open loop and high accuracy, and describes the relationship between the latter and the core-material magnetic properties in the case of Fe-50%Ni alloys. It is pointed out that air-gap precision, nonlinearity B– H and hysteresis are the main sources of accuracy; the influences of mechanical stress and temperature on coercive field are quantified and have to be taken into account in the design of the sensor. It is shown by dedicated choice of grades and annealing that Fe-50%Ni alloys may vary their coercive field from 4–6 A/m down to 1.5–4 A/m depending on the final annealing treatment used.

Flyback Inverter Controlled by Sensorless Current MPPT for Photovoltaic Power System

This paper presents a flyback inverter controlled by sensorless current maximum power point tracking (MPPT) for a small photovoltaic (PV) power system. Although the proposed system has small output power such as 300 W, a few sets of small PV power systems can be easily connected in parallel to yield higher output power. When a PV power system is constructed with a number of small power systems, the total system cost will increase and will be a matter of concern. To overcome this difficulty, this paper proposes a PV system that uses no expensive dc current sensor but utilizes the method of estimating the PV current from the PV voltage. The paper shows that the application of this novel sensorless current flyback inverter to an MPPT-operated PV system exhibits satisfactory MPPT performance similar to the one exhibited by the system with a dc current sensor as well. This paper also deals with the design method and the operation of the unique flyback inverter with center-tapped secondary winding.

Soft magnetic FeNi alloys for DC current sensors with high accuracy

This paper deals with the DC current sensor with closed loop and high accuracy, and describes the relationship between the latter and the core material magnetic properties. The coercive field H c, which controls strongly the sensor accuracy, may fluctuate heavily with operating temperature and external stresses as shown in the cases of three different FeNi alloys. Non-coated Fe–80%Ni exhibit low H c ( < 1 A / m ) : this is kept ( H c ⩽ 1.2 A / m ) under strong external stresses (coating) when a low magnetostriction alloy is used. If coating-induced stresses are avoided, a FeNiCr alloy offers an interesting opportunity to get both good accuracy due to low H c ( ⩽ 2 A / m ) and a cheaper solution.

Excitation circuit for fluxgate sensor using saturable inductor

Traditional excitation circuits for fluxgate sensors consist of a lossy resistor or a bulky inductor (operated in non-saturated mode), whose function is to limit the excitation current. As a result, a high voltage source is required to provide sufficient excitation current to the sensor. For these reasons, traditional excitation circuits are unsuitable for portable battery operated devices that use fluxgate sensors. In order to reduce the circuit size and operating voltage in such applications, the use of a saturable inductor is proposed in this paper. Practical methods for choosing suitable circuit components are described to ensure that the circuit operates under optimum conditions. Experimental results illustrate a good linear relationship between the second harmonic voltage and the measured current for a fluxgate dc current sensor using the proposed excitation circuit.

Commutation Torque Ripple Reduction in Brushless DC Motor Drives Using a Single DC Current Sensor

This paper presents a comprehensive study on reducing commutation torque ripples generated in brushless DC motor drives with only a single DC-link current sensor provided. In such drives, commutation torque ripple suppression techniques that are practically effective in low speed as well as high speed regions are scarcely found. The commutation compensation technique proposed here is based on a strategy that the current slopes of the incoming and the outgoing phases during the commutation interval can be equalized by a proper duty-ratio control. Being directly linked with deadbeat current control scheme, the proposed control method accomplishes suppression of the spikes and dips superimposed on the current and torque responses during the commutation intervals of the inverter. Effectiveness of the proposed control method is verified through simulations and experiments.

Current-Sensor-Less Control of High Frequency Link Type Inverter for Photovoltaic System

It is required to use the DC current sensor in the photovoltaic system which is controlled by the maximum power point tracking. To eliminate this expensive sensor, this paper shows how to estimate DC output current of PV array by using the main capacitor voltage and on-duration of the main semiconductor switch in high frequency link type inverter. The experimental data show the proposed technique is helpful to practical use.

Soft magnetic wires

An overview of the present state of the art on the preparation techniques, outstanding magnetic properties and applications of soft magnetic micro and nanowires is presented. Rapid solidification techniques (in-rotating-water quenching and drawing methods) to fabricate amorphous microwires with diameter in the range from 100 down to 1 μm are first described. Electrodeposition is also employed to prepare composite microtubes (magnetic coatings) and to fill porous membranes (diameter of the order of 0.1 μm). Magnetic behaviours of interest are related to the different hysteresis loops of samples: square-shaped loops typical of bistable behaviour, and nearly non-hysteretic loop with well-defined transverse anisotropy field. The role played by magnetic dipolar interactions in the magnetic behaviour of arrays of micro and nanowires is described. A particular analysis is done on the giant magnetoimpedance (GMI) effect in the radio and microwave frequency ranges exhibited by ultrasoft microwires. Finally, a few examples of applications are introduced for magnetostrictive and non-magnetostrictive wires, they are: “magnetoelastic pens”, micromotors; DC current-sensors based on GMI, and sharpened amorphous wire tips in spin polarised scanning tunneling microscopy.

Portable optical AC- and proposed DC-current sensor for high voltage applications

The design and testing of a passive optical current sensor utilizing the Faraday effect is described. The system, being of the ring core sensor type, is portable and capable of being mounted on existing cables and power lines without disconnection. System performance regarding linearity, temperature dependence and the influence of current conductor displacement relative to the ring core are reported. A proper passive temperature compensation is tested and a scheme for optical measurement of DC-current proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Control Algorithm for the Inverter Fed Induction Motor Drive with DC Current Feedback Loop Based on Principles of the Vector Control

ABSTRACT This paper brings out a control algorithm for VSI fed induction motor drives based on the converter DC link current feedback. It is shown that the speed and flux can be controlled over the wide speed and load range quite satisfactorily for simpler drives. The base commands of both the inverter voltage and frequency are proportional to the reference speed, but each of them is further modified by the signals derived from the DC current sensor. The algorithm is based on the equations well known from the vector control theory, and is aimed to obtain the constant rotor flux and proportionality between the electrical torque, the slip frequency and the active component of the stator current. In this way, the problems of slip compensation, Ri compensation and correction of U/f characteristics are solved in the same time. Analytical considerations and computer simulations of the proposed control structure are in close agreement with the experimental results measured on a prototype drive.

An AC and DC current sensor of high accuracy

A current sensor that can detect AC and DC currents with high accuracy of the same degree is presented. The detection characteristics are not degraded even when the sensor is exposed to large temperature variations and/or to external magnetic fields. The proposed sensor, which is named for the sensing principle it employs, will be referred to as the magnetic field controlled type or the zero magnetic field type of field and has the ability to fulfil the following specifications: (1) the sensor is a noncontacting type; (2) the operating frequency range covers from DC to several hundred hertz; (3) the dynamic range can be extended from several milliamperes to 100 A; (4) a detection accuracy of 0.01% full scale (FS) is guaranteed over the sensor's whole range; and (5) several sets of current sensor having the same detection characteristics are easily obtainable even if the B-H of the core to be used for each sensor is very different.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Amorphous wire magnetic field and DC current sensor based on the inverse Wiedemann effect

A magnetic field sensor is presented which is based on the inverse Wiedemann effect (IWE) on amorphous wires. The external magnetic DC field to be detected changes the time symmetry of the output voltage induced in a pick-up coil, creating even harmonics. Measurement results show important advantages in sensitivity and working frequencies mainly due to the core's geometry. The sensor has outstanding sensitivity for magnetic fields below 0.02 mT, as well as a low working frequency and current intensity. >

A converter-type magnetometer using amorphous ribbon or wire

The accurate and quick-response magnetometer presented here is composed of a resonant circuit with an amorphous core, an operational amplifier, and a voltage-current converter. Nonmagnetostrictive amorphous ribbons or wires are used in the straight form for sensing strength and direction of the dc magnetic field. The range having good linearity strongly depends on the converter current and the demagnetizing field of the core. The maximum sensitivity was around 20 V/Oe and noise level around 10 mV/Oe depending on the alloy composition. A simple electrical model of the magnetometer also has been created. Experimental and analytical results obtained from this model proved to be comparable to that used in the computer-aided designing. A converter-type magnetometer is suitable for applications in the magnetic field and dc current sensors, in displacement transducers, and others.

Sensing and measurement of DC current using a transformer and RL-multivibrator

A circuit for sensing and measurement of DC current using a transformer and RL-multivibrator is proposed. The bridge multivibrator circuit is obtained, connecting the primary coil of a nonlinear transformer to an operational amplifier. The DC current that has to be measured is applied to the secondary of the transformer. It is shown that the DC voltage measured at the inverting node of the operational amplifier gives the information on polarity and value of DC current in the secondary. The transfer characteristic of such a DC current sensor is linear for small values of the measured DC current. >

DC current sensors of instantaneous response using amorphous cores

A new current sensor made of three transistor core multivibrators of high frequency is presented. Three multivibrators are synchronized with external pulses so that rectangular three phase voltages may be obtained. The core flux in each multivibrator changes along the minor hysteresis loop. We have no ripple dc output voltage from the outputs of the three multivibrators in the same way as that of a mixing amplifier. The amorphous cores with excellent rectangularity are effectively used for this purpose.