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1、1776IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 24, NO. 7, JULY 2009Wideband Current Transducer for Measuring AC Signals With Limited DC OffsetMichael Hartmann, Student Member, IEEE, Juergen Biela, Member, IEEE, Hans Ertl, Member, IEEE, and Johann W. Kolar, Senior Member, IEEEAbstractIn many applic
2、ations, a current measurement that can measure ac currents with dc offset is required. This is not possible using conventional current transformers (CTs) due to the core saturation because of the dc offset. In this paper, a new sen- sor concept is presented, which consists of a wideband CT and a dem
3、agnetizing circuit. The sensor concept is capable of measuring ac currents with dc offset, which have periodic zero crossings, as given in power-factor-corrected (PFC) circuits. Using the demag- netization circuit, the core is actively reset during the zero crossing intervals. The operation principl
4、e and design equations are dis- cussed in detail in this paper. For validating the presented concept, three sensors have been built using different core materials, and measurements of the transfer functions as well as operation in a PFC system are presented. A bandwidth from dc up to 20 MHz has been
5、 achieved.IndexTermsCurrentmeasurement,currenttransformer(CT), nanocrystalline material.I. INTRODUCTION AN INCREASING number of power electronic systems connected to the power grid, such as input stages of tele- com power supplies 1, 2, front-end systems of drives 3, or power electronics for renewab
6、le energy sources 4, 5, arerealized with active rectifier circuit topologies. In order to min-imize the influence on the mains, sinusoidal input currents and a unity power factor are required. A current controller is used to achieve these requirements, for which the input currents must be measured (
7、cf., Fig. 1). Additionally, a superimposed volt- age or load regulation is applied, which is not shown in Fig. 1 for simplicity. In contrast to single-phase systems with a typ- ical power level below 1 kW, where often shunt resistors are used for current measurement, a galvanically isolated current
8、measurement is required for higher power levels, where usu- ally three-phase systems are utilized. Such a concept offers the advantage of lower losses, since usually no shunt resistors are used, and measurement signals that can be processed directly by the digital signal processor. Therefore, it is
9、very important that the current sensor should also measure dc currents besides the ac component in order to guarantee dc-free mains currents.Manuscript received August 29, 2008; revised November 28, 2008. Current version published July 29, 2009. Recommended for publication by Associate Editor C. R.
10、Sullivan. M. Hartmann, J. Biela, and J. W. Kolar are with the Power Electronic Sys- temsLaboratory,SwissFederalInstituteofTechnology(ETH)Zurich,CH-8092 Zurich, Switzerland (e-mail: hartmannlem.ee.ethz.ch; bielalem.ee.ethz.ch; kolarlem.ee.ethz.ch). H. Ertl is with the Power Electronics Section, Vienn
11、a University of Technol- ogy, A-1040 Vienna, Austria (e-mail: j.ertltuwien.ac.at).Digital Object Identifier 10.1109/TPEL.2009.2017263Fig. 1.AC/DC converter with sinusoidally controlled input currents. In order to guarantee dc-free input currents, a current sensor that can measure the ac and dc compo
12、nents of the input current has to be used.Fig. 2.Classification of isolated current measurement principles.The general trend for higher power densities is driven by cost reduction, an increased functionality, and limited weight/space, in some applications (e.g., automotive and aircraft) 6. Thisfinal
13、ly results in constantly increasing switching frequencies, whichcomesalongwithanincreasedbandwidthrequirementfor the current sensor. In particular, control strategies such as direct powercontrol7ordecoupledhysteresiscontrol8,9,where the switching instants are directly derived from the measured curre
14、nts, require exact knowledge of the current ripple. Also, in aircraft power supplies, which have very rigid requirements on the total harmonic distortion (THD T. This is veryuseful, if the sensor is located on the dc side of the rectifier Fig. 18(c), since the current to be measured includes a signi
15、f- icant dc component, as illustrated in Fig. 3(a). In order to retain a small core size, the CT must then be demagnetized every half period of the mains. InFig.3(c),theproposedsensorconceptisappliedtoaphase-leg of a Vienna rectifier structure. Here, two CTs are used and one CT is placed in each dio
16、de path, which only conducts for half a period. No additional switch is required here as the time intervalwithzerocurrentisinherentlyusedfordemagnetization.HARTMANN et al.: WIDEBAND CURRENT TRANSDUCER FOR MEASURING AC SIGNALS WITH LIMITED DC OFFSET1779Fig. 5.Equivalent circuits of the CT with demagnetizing cicuit including (a) parasitic elements and (b) low-frequency equivalent circuit for closed switch S2.A. Model of the Current TransformerIn order to be able to desig
