JPH10274665A - Current detector - Google Patents
Current detectorInfo
- Publication number
- JPH10274665A JPH10274665A JP9094594A JP9459497A JPH10274665A JP H10274665 A JPH10274665 A JP H10274665A JP 9094594 A JP9094594 A JP 9094594A JP 9459497 A JP9459497 A JP 9459497A JP H10274665 A JPH10274665 A JP H10274665A
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- Japan
- Prior art keywords
- current
- output
- input
- amplifier
- operational amplifier
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Transformers For Measuring Instruments (AREA)
- Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
- Measurement Of Current Or Voltage (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、変流器、即ち電流
トランス（ＣＴ）を用いた電流検出装置に関し、特に、
外来雑音の影響を軽減した電流検出装置に関するもので
ある。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detector using a current transformer, that is, a current transformer (CT).
The present invention relates to a current detection device that reduces the influence of external noise.
【０００２】[0002]
【従来の技術】電流トランス（ＣＴ）とはカレント・ト
ランスを略したもので、変流器とも呼ばれ、電力関係で
は、大電流を測定するための電流変成器（計器用変成
器）として広く使用されている。図３には、かかる電流
トランスの簡略図が示されている。図３において、環状
の閉磁路に数１００ターンから２０００ターン程度の２
次巻線を巻回し、同閉磁路内を貫通させた１次線に被測
定電流ｉsを貫通電流として流す。磁路の形状としては
トロイダル巻線を施したものが漏洩磁束の低減や小型化
を図るのに有効である。そして、２次巻線に流れる電流
を検出して被測定電流を検出する。2. Description of the Related Art A current transformer (CT) is an abbreviation of a current transformer, and is also called a current transformer. In terms of power, it is widely used as a current transformer (meter transformer) for measuring a large current. It is used. FIG. 3 shows a simplified diagram of such a current transformer. In FIG. 3, the circular closed magnetic path has two hundreds to 2,000 turns.
A current to be measured is is passed as a through current to a primary wire wound around the secondary winding and penetrating through the closed magnetic path. The shape of the magnetic path provided with a toroidal winding is effective for reducing the leakage magnetic flux and reducing the size. Then, a current to be measured is detected by detecting a current flowing through the secondary winding.
【０００３】図４には、図３に示すような電流トランス
を電流センサとして用いた従来型の電流検出装置の回路
構成が示されている。電流トランス（ＣＴ）１の１次線
に検出電流ｉsを流すと、２次巻線に電流が誘起され、
この電流はオペアンプ２の反転入力に供給される。オペ
アンプ２の反転入力と出力間には帰還抵抗Ｒfが接続さ
れ、その非反転入力は接地される。この抵抗Ｒfには電
流トランス１の２次巻線に流れる電流と同じ大きさの電
流が流れる。FIG. 4 shows a circuit configuration of a conventional current detecting device using a current transformer as shown in FIG. 3 as a current sensor. When the detection current is flows through the primary line of the current transformer (CT) 1, a current is induced in the secondary winding,
This current is supplied to the inverting input of the operational amplifier 2. A feedback resistor Rf is connected between the inverting input and the output of the operational amplifier 2, and the non-inverting input is grounded. A current having the same magnitude as the current flowing through the secondary winding of the current transformer 1 flows through the resistor Rf.
【０００４】今、検出電流をｉs、電流トランス１の変
流比をｋとすると、２次巻線には電流（ｋ・ｉs）が流
れるので、オペアンプ２の信号出力電圧にはｖos＝（ｋ
・ｉs）Ｒfなる電圧が現われる。Now, assuming that the detected current is is and the current transformer 1 has a current transformation ratio of k, a current (k · is) flows through the secondary winding, so that the signal output voltage of the operational amplifier 2 has vos = (k
・ Is) A voltage Rf appears.
【０００５】[0005]
【発明が解決しようとする課題】上述のような従来の回
路構成により、大電流の測定が可能であるが、図４に示
す従来の回路は次のような欠点をもつ。即ち、電流トラ
ンス１の入力側と接地間の浮遊容量Ｃsを介して同相モ
ードの雑音電圧ｖnが電流トランス１の２次側に混入す
るため、微小電流検出が困難となるという問題である。
例えば、図４において、同相モード雑音電圧ｖnにより
オペアンプ２の出力に現われる雑音出力電圧は、ｖon＝
ｖn・ωＣs・Ｒfとなる。Although a large current can be measured by the above-described conventional circuit configuration, the conventional circuit shown in FIG. 4 has the following disadvantages. That is, since the noise voltage vn in the common mode is mixed into the secondary side of the current transformer 1 via the stray capacitance Cs between the input side of the current transformer 1 and the ground, it is difficult to detect a minute current.
For example, in FIG. 4, the noise output voltage appearing at the output of the operational amplifier 2 due to the common mode noise voltage vn is von =
vn · ωCs · Rf.
【０００６】そこで、本発明の目的は、電流トランスを
用いた電流検出の際の同相雑音成分の重畳の影響を除去
できる電流検出装置を提供することにある。SUMMARY OF THE INVENTION It is an object of the present invention to provide a current detection device capable of removing the influence of superimposition of a common-mode noise component at the time of current detection using a current transformer.
【０００７】本発明の他の目的は、上記目的に追加して
更に直流ドリフトの問題を解決できる電流検出装置を提
供することにある。Another object of the present invention is to provide a current detection device which can solve the problem of DC drift in addition to the above objects.
【０００８】[0008]
【課題を解決するための手段】上述の問題点を解決する
ため、本発明による電流検出装置は、変流器の入力側に
流れる検出電流に対応して出力側に流れる電流を検出す
ることにより前記検出電流を検出する電流検出装置にお
いて、前記変流器の出力を電流入力型の差動増幅手段を
用いて取り出す。In order to solve the above-mentioned problems, a current detecting device according to the present invention detects a current flowing to an output side corresponding to a detected current flowing to an input side of a current transformer. In the current detection device for detecting the detection current, the output of the current transformer is extracted by using a current input type differential amplifier.
【０００９】本発明の他の態様による電流検出装置は、
変流器の入力側に流れる検出電流に対応して出力側に流
れる電流を検出することにより前記検出電流を検出する
電流検出装置において、前記変流器の出力に接続され、
入力端子に流れる電流に比例した出力を生じる差動増幅
器からなる電流入力型差動増幅手段と、該電流入力型差
動増幅手段の出力段から前記電流入力型差動増幅手段の
入力段に直流帰還を施す直流帰還手段とを備えて成る。According to another aspect of the present invention, there is provided a current detecting device comprising:
In a current detection device that detects the detection current by detecting a current flowing to an output side corresponding to a detection current flowing to an input side of the current transformer, the current detection device is connected to an output of the current transformer,
Current input type differential amplifying means comprising a differential amplifier which produces an output proportional to the current flowing through the input terminal; and a direct current from an output stage of the current input type differential amplifying means to an input stage of the current input type differential amplifying means. DC feedback means for performing feedback.
【００１０】本発明の更に、他の態様による電流検出装
置は、変流器の入力側に流れる検出電流に対応して出力
側に流れる電流を検出することにより前記検出電流を検
出する電流検出装置において、前記変流器出力の一方の
端子に接続された第１の電流入力増幅器と、前記変流器
出力の他方の端子に接続された第２の電流入力増幅器と
を備え、前記一方の端子と前記第１の電流入力増幅器と
の接続点に前記第２の電流入力増幅器の出力を注入する
ことにより、浮遊容量を介して前記変流器に誘起した雑
音成分を打ち消している。A current detecting device according to still another aspect of the present invention is a current detecting device for detecting the detected current by detecting a current flowing to an output side corresponding to a detected current flowing to an input side of a current transformer. , A first current input amplifier connected to one terminal of the current transformer output, and a second current input amplifier connected to the other terminal of the current transformer output, wherein the one terminal By injecting the output of the second current input amplifier into a connection point between the current input amplifier and the first current input amplifier, a noise component induced in the current transformer via a stray capacitance is canceled.
【００１１】ここで、前記第１の電流入力増幅器の出力
から前記第１の電流入力増幅器の入力へ直流帰還を施す
直流帰還手段を有する。Here, there is provided DC feedback means for performing DC feedback from the output of the first current input amplifier to the input of the first current input amplifier.
【００１２】[0012]
【発明の実施の形態】以下、図面を参照しながら本発明
による電流検出装置の実施形態を説明する。図１は本発
明による電流検出装置の一実施形態を示す回路図であ
る。本実施形態では、検出電流ｉsを電流トランス（電
流センサ）の１次側に流して２次側に流れる電流を電流
入力型の差動アンプで受けて雑音成分をキャンセルする
とともに、オペアンプ５等で構成される積分器を用いて
出力から入力に直流帰還を施すことによりドリフト特性
を改善している。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the current detecting device according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a current detection device according to the present invention. In the present embodiment, the detection current is flows to the primary side of the current transformer (current sensor), and the current flowing to the secondary side is received by a current input type differential amplifier to cancel noise components. The drift characteristic is improved by applying DC feedback from the output to the input using the integrator configured.
【００１３】図１において、同相モード雑音ｖnは、図
中の浮遊容量Ｃs1、Ｃs2を介して電流センサ１の２次巻
線に重畳し悪影響を及ぼす。同相モード雑音ｖnは、説
明の都合上、等価的にこのような雑音電圧が存在するこ
とを示したものであり、実際の電流検出装置においては
ｖnなる雑音電圧源を用意する必要はない。電流トラン
ス（カレントトランス＝ＣＴ）型の電流センサ１の２次
巻線の出力端子１１、１２には１次側の貫通電流、即ち
検出電流（ｉs）に比例した電流が流れる。電流センサ
１の一方の端子１１は、オペアンプ３の反転入力（−）
に接続されている。他方の端子１２はオペアンプ４の反
転入力（−）に接続されている。In FIG. 1, common-mode noise vn is superimposed on the secondary winding of the current sensor 1 via stray capacitances Cs1 and Cs2 in the figure, and has an adverse effect. The common-mode noise vn indicates that such a noise voltage is equivalently present for convenience of explanation, and it is not necessary to prepare a noise voltage source vn in an actual current detection device. A primary-side through current, that is, a current proportional to the detection current (is) flows through the output terminals 11 and 12 of the secondary winding of the current sensor 1 of a current transformer (current transformer = CT) type. One terminal 11 of the current sensor 1 is connected to the inverting input (−) of the operational amplifier 3.
It is connected to the. The other terminal 12 is connected to the inverting input (−) of the operational amplifier 4.
【００１４】オペアンプ３と４の反転入力（−）と出力
との間には帰還抵抗Ｒf1、Ｒf2がそれぞれ接続されてい
る。オペアンプ３と４の非反転入力（＋）にはオフセッ
ト電流を補償する抵抗Ｒ６とＲ７がそれぞれ接続され、
接地されている。Feedback resistors Rf1 and Rf2 are connected between the inverted inputs (-) and the outputs of the operational amplifiers 3 and 4, respectively. Non-inverting inputs (+) of the operational amplifiers 3 and 4 are connected to resistors R6 and R7 for compensating offset current, respectively.
Grounded.
【００１５】オペアンプ３と４の出力は、抵抗Ｒ１〜Ｒ
４及びオペアンプ２から成る差動アンプの反転入力と非
反転入力にそれぞれ入力され、オペアンプ２の出力から
電圧出力ｖOが取り出される。オペアンプ２の出力には
抵抗Ｒ５が接続され、この抵抗Ｒ５の他端はオペアンプ
５の反転入力（−）に接続されている。オペアンプ５の
反転入力（−）と出力間にはキャパシタＣ１が接続さ
れ、非反転入力（＋）は接地されている。The outputs of the operational amplifiers 3 and 4 are connected to resistors R1 to R
4 and a non-inverting input of a differential amplifier composed of the operational amplifier 2, and a voltage output vO is extracted from the output of the operational amplifier 2. A resistor R5 is connected to the output of the operational amplifier 2, and the other end of the resistor R5 is connected to the inverting input (-) of the operational amplifier 5. The capacitor C1 is connected between the inverting input (-) and the output of the operational amplifier 5, and the non-inverting input (+) is grounded.
【００１６】オペアンプ５の出力は、抵抗Ｒ８を経由し
てオペアンプ４の非反転入力（＋）に接続され、オペア
ンプ２の出力に現われる直流ドリフトを負帰還によりキ
ャンセルしている。The output of the operational amplifier 5 is connected to the non-inverting input (+) of the operational amplifier 4 via the resistor R8, and cancels the DC drift appearing at the output of the operational amplifier 2 by negative feedback.
【００１７】こうして、オペアンプ２の出力には、電流
センサ１の端子１１−１２に流れる電流に比例した電圧
が現われる。今、電流センサ１の貫通電流をｉs、電流
センサ１の変流比をｋとすると、２次巻線に流れる電流
はｉs・ｋとなり、オペアンプ３の帰還抵抗の抵抗値を
Ｒf1、オペアンプ４の帰還抵抗値Ｒf2とすると、オペア
ンプ２の反転入力と非反転入力に供給される電圧ｖs1、
ｖs2はそれぞれ次のようになる。 ｖs1＝ （ｉs・ｋ）Ｒf1 （１） ｖs2＝−（ｉs・ｋ）Ｒf2 （２）Thus, a voltage proportional to the current flowing through the terminals 11-12 of the current sensor 1 appears at the output of the operational amplifier 2. Now, assuming that the through current of the current sensor 1 is is and the current conversion ratio of the current sensor 1 is k, the current flowing through the secondary winding is is · k, the resistance value of the feedback resistor of the operational amplifier 3 is Rf1, and the current value of the operational amplifier 4 is Assuming that the feedback resistance value is Rf2, the voltage vs1 supplied to the inverting input and the non-inverting input of the operational amplifier 2,
vs2 is as follows. vs1 = (is · k) Rf1 (1) vs2 = − (is · k) Rf2 (2)
【００１８】このｖs1、ｖs2がオペアンプ２で構成され
る差動アンプに入力される。抵抗Ｒ１〜Ｒ４の抵抗値を
等しくすれば、この段の利得は１となり、Ｒf1＝Ｒf2＝
Ｒfとすると、出力出圧ｖoは次式のようになる。 ｖo＝（ｖs1−ｖs2）＝２（ｉs・ｋ）Ｒf （３）The signals vs1 and vs2 are input to a differential amplifier composed of an operational amplifier 2. If the resistance values of the resistors R1 to R4 are made equal, the gain of this stage becomes 1, and Rf1 = Rf2 =
Assuming Rf, the output pressure vo is given by the following equation. vo = (vs1−vs2) = 2 (is · k) Rf (3)
【００１９】今、貫通電流ｉs＝１〔Ａ〕、２次巻数ｎ
＝７１９、帰還抵抗Ｒf＝３．５９５ｋΩとすると、ｋ
＝１／ｎであるから、ｖoは１０〔V/A〕となる。Now, the through current is = 1 [A], the number of secondary turns n
= 719 and feedback resistance Rf = 3.595 kΩ, k
Since = 1 / n, vo becomes 10 [V / A].
【００２０】一方、同相モードの雑音電圧ｖnについて
は上記ｖn1、ｖn2はそれぞれ次のようになる。 ｖn1＝−ｖn・ｊωＣs1・Ｒf1 （４） ｖn2＝−ｖn・ｊωＣs2・Ｒf2 （５） このｖn1、ｖn2は、次段の差動アンプに入力されるの
で、ｖn1＝ｖn2であれば、出力に同相モードの雑音電圧
は現われない。その条件は次の通りである。 Ｒf1・Ｃs1＝Ｒf2・Ｃs2 （６）On the other hand, with respect to the noise voltage vn in the common mode, vn1 and vn2 are as follows. vn1 = −vn · jωCs1 · Rf1 (4) vn2 = −vn · jωCs2 · Rf2 (5) Since vn1 and vn2 are input to the differential amplifier at the next stage, if vn1 = vn2, the output is in phase. No mode noise voltage appears. The conditions are as follows. Rf1 · Cs1 = Rf2 · Cs2 (6)
【００２１】通常、浮遊容量Ｃs1、Ｃs2の値は等しくな
いため、式（６）の条件を満足するようにＲf1あるいは
Ｒf2に可変抵抗器を直列に接続してこれを調整し、Ｃs
1、Ｃs2のバラつきを補償する。Normally, since the values of the stray capacitances Cs1 and Cs2 are not equal, a variable resistor is connected in series to Rf1 or Rf2 so as to satisfy the condition of the equation (6), and this is adjusted.
1. Compensate for variations in Cs2.
【００２２】以上のような構成により、電流トランスの
入出力間の浮遊容量に起因して生ずる雑音成分ｖnの影
響は除去できる。一方、電流入力型の差動増幅器の導入
に伴い、この増幅器の直流利得が極端に増加するため直
流ドリフトが新たな問題となる。With the above configuration, the effect of the noise component vn caused by the stray capacitance between the input and output of the current transformer can be eliminated. On the other hand, with the introduction of a current input type differential amplifier, the DC gain of this amplifier increases extremely, so that DC drift becomes a new problem.
【００２３】より具体的には、本実施形態では、上述の
ように、オペアンプ５、抵抗Ｒ５及びキャパシタＣ１か
ら成る回路は積分器を構成しており、オペアンプ２の出
力の交流成分を除去し直流成分を取り出している。かか
るオペアンプ５による直流帰還効果は次のとおりであ
る。More specifically, in the present embodiment, as described above, the circuit including the operational amplifier 5, the resistor R5, and the capacitor C1 forms an integrator, and removes the AC component of the output of the operational amplifier 2 and removes the DC component. The components are taken out. The DC feedback effect of the operational amplifier 5 is as follows.
【００２４】電流センサ１の２次巻線の直流抵抗は種類
にもよるが普通は数１０Ω以下である。一方、オペアン
プ３による電流−電圧変換回路の帰還抵抗Ｒf1は通常数
ｋΩである。そしてこの段の直流利得はＧ＝Ｒf1／Ｒi
で表わされ、入力抵抗Ｒiは前述の２次巻線の直流抵抗
であるから、結局この段の直流利得は１００倍のオーダ
となる。The DC resistance of the secondary winding of the current sensor 1 depends on the type, but is usually several tens of ohms or less. On the other hand, the feedback resistance Rf1 of the current-to-voltage conversion circuit by the operational amplifier 3 is usually several kΩ. And the DC gain of this stage is G = Rf1 / Ri
Since the input resistance Ri is the DC resistance of the secondary winding described above, the DC gain of this stage is eventually on the order of 100 times.
【００２５】このため、この電流−電圧変換回路のオペ
アンプに安価な汎用オペアンプを使用すると温度ドリフ
トが大きくなり使いものにならない。また温度ドリフト
の小さいオペアンプを使用すると、そのようなオペアン
プは非常に高価であるためコストがアップするという問
題が発生する。For this reason, if an inexpensive general-purpose operational amplifier is used as the operational amplifier of the current-voltage conversion circuit, the temperature drift becomes large and the operational amplifier cannot be used. Further, when an operational amplifier having a small temperature drift is used, such an operational amplifier is very expensive, so that there is a problem that the cost is increased.
【００２６】本実施形態では、かかる問題を解決するた
め、出力から初段にオペアンプ５による直流帰還を施し
温度ドリフトを軽減している。その結果、オペアンプ
３、４に安価なオペアンプを使用しても十分満足できる
温度ドリフト特性が得られる。In the present embodiment, in order to solve such a problem, a direct current feedback by the operational amplifier 5 is performed from the output to the first stage to reduce the temperature drift. As a result, sufficiently satisfactory temperature drift characteristics can be obtained even if inexpensive operational amplifiers are used for the operational amplifiers 3 and 4.
【００２７】図２は本発明による電流検出装置の他の実
施形態を示す要部回路図であり、説明の都合上、浮遊容
量Ｃs1、Ｃs2及び同相モード雑音電圧ＶNが記入されて
いる。本実施形態は、図１に示す実施形態と同様に、電
流トランス（ＣＴ）型の電流センサ１に流れる電流を出
力電圧ｖoに変換して出力するもので、等価的に同様な
機能を果たすが、使用オペアンプを４個から３個に、使
用抵抗を１０個から７個に低減できる。FIG. 2 is a main part circuit diagram showing another embodiment of the current detecting device according to the present invention. For convenience of explanation, stray capacitances Cs1, Cs2 and a common mode noise voltage VN are shown. The present embodiment converts the current flowing through the current transformer (CT) type current sensor 1 into an output voltage vo and outputs the same, similarly to the embodiment shown in FIG. 1. The number of operational amplifiers used can be reduced from four to three, and the number of used resistors can be reduced from ten to seven.
【００２８】電流トランス型の電流センサ１、閉磁路に
２次巻線（出力端子１１、１２）を巻回し、１次線は閉
磁路内を貫通させて使用される。貫通電流に比例した電
流が２次巻線に誘起される。オペアンプ６の反転入力
は、電流センサ１の一方の出力端子１１に接続され、オ
ペアンプ６の出力と反転入力（−）との間には抵抗Ｒ１
０１と浮遊容量Ｃ１０１の並列回路が接続されている。
抵抗Ｒ１０１は帰還抵抗（Ｒf1）であり、電流センサ１
の２次側に流れる電流はオペアンプ６により電圧に変換
され、出力電圧ｖoが出力される。A current transformer type current sensor 1 is used in which a secondary winding (output terminals 11 and 12) is wound around a closed magnetic path, and a primary wire is passed through the closed magnetic path. A current proportional to the through current is induced in the secondary winding. The inverting input of the operational amplifier 6 is connected to one output terminal 11 of the current sensor 1, and a resistor R1 is connected between the output of the operational amplifier 6 and the inverting input (-).
01 and a stray capacitance C101 are connected in parallel.
The resistor R101 is a feedback resistor (Rf1), and the current sensor 1
Is converted into a voltage by the operational amplifier 6, and an output voltage vo is output.
【００２９】電流センサ１１の他方の端子１２は、オペ
アンプ７の反転入力（−）に接続されている。オペアン
プ７の出力と反転入力（−）との間には抵抗Ｒ１０２
（抵抗Ｒf2）とキャパシタＣ１０２の並列回路が接続さ
れている。オペアンプ７の非反転入力（＋）はＲ１０６
を経て接地されている。オペアンプ７の出力は、抵抗Ｒ
１０３とキャパシタＣ１０３の並列回路を介してオペア
ンプ６の反転入力（−）に接続されている。The other terminal 12 of the current sensor 11 is connected to the inverting input (-) of the operational amplifier 7. A resistor R102 is provided between the output of the operational amplifier 7 and the inverted input (−).
A parallel circuit of (resistor Rf2) and capacitor C102 is connected. The non-inverting input (+) of the operational amplifier 7 is R106
Through the ground. The output of the operational amplifier 7 is a resistor R
It is connected to the inverting input (-) of the operational amplifier 6 through a parallel circuit of the capacitor 103 and the capacitor C103.
【００３０】オペアンプ６の出力は、抵抗Ｒ１０５を介
してオペアンプ８の反転入力（−）に接続されている。
オペアンプ８の出力と反転入力(−)との間にはキャパシ
タＣ１０５が接続されている。オペアンプ８、抵抗Ｒ１
０５、キャパシタＣ１０５から成る回路は積分回路を構
成し、抵抗Ｒ１０５とキャパシタＣ１０５の値の積で計
算される時定数を秒のオーダとすることにより出力ｖo
中の直流成分を抽出している。そして、これをオペアン
プ６の非反転入力（＋）に負帰還することにより、出力
ｖoに現われるドリフトをキャンセルしている。こうす
ることにより、上述実施形態の説明で述べたのと同じ理
由によりオペアンプ６と７の直流利得が非常に大きくな
り、結果として出力に多大のドリフトが発生するという
問題点が除去される。The output of the operational amplifier 6 is connected to the inverting input (-) of the operational amplifier 8 via the resistor R105.
A capacitor C105 is connected between the output of the operational amplifier 8 and the inverted input (-). Operational amplifier 8, resistor R1
05, the circuit comprising the capacitor C105 forms an integrating circuit, and the output vo is obtained by setting the time constant calculated by the product of the value of the resistor R105 and the value of the capacitor C105 to the order of seconds.
The DC component inside is extracted. This is negatively fed back to the non-inverting input (+) of the operational amplifier 6 to cancel the drift appearing at the output vo. This eliminates the problem that the DC gains of the operational amplifiers 6 and 7 become extremely large for the same reason as described in the description of the above embodiment, and as a result, a large drift occurs in the output.
【００３１】電流センサ１の２次巻線に流れる信号電流
ｉｓｓについて考えると、出力端子１２から流出する電
流は、オペアンプ７で極性反転され、Ｒ１０３を経由し
てオペアンプ６の反転入力（仮想接地点）に注入され
る。ここでＲ１０３に流れる電流はｉssと極性が同じで
あるため、信号電流を増大するように作用する。Considering the signal current iss flowing in the secondary winding of the current sensor 1, the current flowing out of the output terminal 12 is inverted in polarity by the operational amplifier 7, and is input to the inverted input (virtual ground point) of the operational amplifier 6 via R103. ) Is injected. Here, since the current flowing through R103 has the same polarity as iss, it acts to increase the signal current.
【００３２】次に雑音である同相モード雑音電圧ＶNの
影響を考える。まず電流センサ１の出力端子１１には浮
遊容量Ｃs1を介して同相雑音成分が現われる。一方、前
記ＶNのうちＣS2を経由して電流センサ１の出力端子１
２に現われる同相雑音成分はオペアンプ７で反転され、
逆位相となりオペアンプ６の反転入力に注入される。こ
のため信号路である出力端子１１に現われるＣS1経由の
ＶN成分はキャンセルされる。Next, the influence of the common mode noise voltage VN, which is noise, will be considered. First, a common-mode noise component appears at the output terminal 11 of the current sensor 1 via the stray capacitance Cs1. On the other hand, the output terminal 1 of the current sensor 1 via CS2 of the VN
2 is inverted by the operational amplifier 7,
The phase is reversed and injected into the inverting input of the operational amplifier 6. Therefore, the VN component via the CS1 appearing at the output terminal 11, which is a signal path, is canceled.
【００３３】以下では、上記で定性的に説明した浮遊容
量Ｃs1、Ｃs2を介して、信号に重畳する同相モード雑音
電圧について定量的な観点で説明する。In the following, the common-mode noise voltage superimposed on a signal via the stray capacitances Cs1 and Cs2 qualitatively described above will be described from a quantitative viewpoint.
【００３４】図２に示すように、電流センサ１の１次側
（貫通電流）には同相モード雑音電圧ＶNが重畳してい
るものとすると、次の基本式が成立する。 ｉs1＝jωＣs1・ＶN （７）As shown in FIG. 2, assuming that the common mode noise voltage VN is superimposed on the primary side (through current) of the current sensor 1, the following basic formula is established. is1 = jωCs1 · VN (7)
【００３５】回路が正常に動作している場合には、オペ
アンプ６と７の非反転入力（＋）は交流的にはゼロ電位
である。また、オペアンプの性質より反転入力（−）も
交流的にゼロ電位である。すると、出力端子１１、１２
はともに同電位なのでＣｓｔには交流電流は流れず、ｉ
st＝０となりＣstの影響は考えなくてよい。このため次
の関係式が成立する。 ｉs2＝jωＣs2・ＶN （８） ｖ2 ＝ −Ｚ2(ｉss＋ｉs2) （９） ｖo＝Ｚ1(ｉss−ｉs1−(ｖ2／Ｚ3)) （１０） ここでＺ1＝Ｒ101//Ｃ101、Ｚ2＝Ｒ102//Ｃ102、Ｚ3＝
Ｒ103//Ｃ103である。（ａ//ｂは、ａとｂの並列接続を
表わす）When the circuit is operating normally, the non-inverting inputs (+) of the operational amplifiers 6 and 7 are zero potential in terms of AC. The inverting input (-) also has an AC zero potential due to the nature of the operational amplifier. Then, the output terminals 11 and 12
Are the same potential, no AC current flows through Cst and i
Since st = 0, there is no need to consider the influence of Cst. Therefore, the following relational expression holds. is2 = jωCs2 · VN (8) v2 = −Z2 (iss + is2) (9) vo = Z1 (iss−is1− (v2 / Z3)) (10) where Z1 = R101 // C101 and Z2 = R102 // C102 , Z3 =
R103 // C103. (A // b represents a parallel connection of a and b)
【００３６】基本式（７）〜（１０）から、ｉs1、ｉs
2、ｖ2を消去してｖoを求めると、次のようになる。From the basic formulas (7) to (10), is1, is
2. When vo is obtained by deleting v2, the following is obtained.
【数１】 (Equation 1)
【００３７】ここで信号と雑音との関係のみに着目する
ため、（１１）式の右辺からＶNを含む項のみを取り出
すと次のようになるHere, in order to focus only on the relationship between the signal and the noise, if only the term including VN is extracted from the right side of the equation (11), the following is obtained.
【数２】 (Equation 2)
【００３８】ここで、τ1=C101・R101、τ2=C102・R102、
τs02=(C102・Cs1-C103・Cs2)・R102・R103、τs1=(Cs1・R10
3-Cs2・R102)、τs2=τs02/τs1である。（１３）、（１
４）式より、ｖｏ/ＶN＝０とするにはτs1及びτs02を
ゼロとすれば良い事ががわかる。即ち、次の関係式が導
かれる。Here, τ1 = C101 · R101, τ2 = C102 · R102,
τs0 2 = (C102 ・ Cs1-C103 ・ Cs2) ・ R102 ・ R103, τs1 = (Cs1 ・ R10
3-Cs2 · R102), is a τs2 = τs0 2 / τs1. (13), (1
4) from the equation, to the vo / VN = 0 is seen be may be set to zero τs1 and τs0 2. That is, the following relational expression is derived.
【数３】 (Equation 3)
【００３９】実際の調整にあたっては、例えば、雑音電
圧ＶNとして矩形波信号を印加し、最初に抵抗Ｒ102、Ｒ
103の比を調整して浮遊容量ＣS1、ＣS2の影響をキャン
セルして（１５）式を満足させる。次にＣ102、Ｃ103を
調整して（１６）式を満足させる。このように調整を行
えば、浮遊容量Ｃs1、Ｃs2を介しての同相モード雑音電
圧の侵入を阻止できる。In the actual adjustment, for example, a rectangular wave signal is applied as the noise voltage VN, and the resistors R102 and R102 are first applied.
By adjusting the ratio of 103, the influence of the stray capacitances CS1 and CS2 is canceled to satisfy the expression (15). Next, C102 and C103 are adjusted to satisfy the expression (16). By performing such adjustment, the intrusion of the common-mode noise voltage through the stray capacitances Cs1 and Cs2 can be prevented.
【００４０】また、この回路はオペアンプ８による直流
帰還の効果により、オペアンプ６と７の非反転入力
（＋）は直流的にはゼロ電位であるため、電流センサ１
の２次巻線に直流が流れない。Further, in this circuit, the non-inverting inputs (+) of the operational amplifiers 6 and 7 are zero potential in terms of direct current due to the effect of DC feedback by the operational amplifier 8, so that the current sensor 1
DC does not flow through the secondary winding.
【００４１】[0041]
【発明の効果】以上説明したように、本発明による電流
検出装置では、電流トランス（ＣＴ）タイプの電流セン
サの出力を電流入力型の差動増幅手段で検出しているた
め、同相モードの雑音電圧が浮遊容量を介して電流セン
サの２次側に注入されたとしても、この雑音電圧は同相
成分であるため差動増幅器によりキャンセルされ出力に
は現われない。更に、直流利得の増大に伴う出力ドリフ
トを直流帰還回路を付加して抑圧しているので、検出電
流のダイナミックレンジを飛躍的に増大させることがで
きる。As described above, in the current detecting device according to the present invention, the output of the current transformer (CT) type current sensor is detected by the current input type differential amplifying means. Even if a voltage is injected into the secondary side of the current sensor via the stray capacitance, the noise voltage is a common-mode component and is canceled by the differential amplifier and does not appear at the output. Further, the output drift accompanying the increase in the DC gain is suppressed by adding a DC feedback circuit, so that the dynamic range of the detection current can be dramatically increased.
【図１】本発明による電流検出装置の実施形態を示す回
路図である。FIG. 1 is a circuit diagram showing an embodiment of a current detection device according to the present invention.
【図２】本発明による電流検出装置の他の実施形態を示
す回路図である。FIG. 2 is a circuit diagram showing another embodiment of the current detection device according to the present invention.
【図３】電流トランスの簡略図である。FIG. 3 is a simplified diagram of a current transformer.
【図４】図３に示す電流トランスを電流センサとして用
いた従来型の電流検出装置の回路構成である。4 is a circuit configuration of a conventional current detection device using the current transformer shown in FIG. 3 as a current sensor.
１ 電流センサ ２〜８ オペアンプ 1 Current sensor 2-8 Operational amplifier
Claims (4)
て出力側に流れる電流を検出することにより前記検出電
流を検出する電流検出装置において、 前記変流器の出力を電流入力型の差動増幅手段を用いて
取り出すことを特徴とする電流検出装置。1. A current detecting device for detecting a detected current by detecting a current flowing on an output side corresponding to a detected current flowing on an input side of a current transformer, wherein an output of the current transformer is a current input type. A current detecting device for extracting the current using the differential amplifying means.
て出力側に流れる電流を検出することにより前記検出電
流を検出する電流検出装置において、 前記変流器の出力に接続され、入力端子に流れる電流に
比例した出力を生じる差動増幅器からなる電流入力型差
動増幅手段と、該電流入力型差動増幅手段の出力段から
前記電流入力型差動増幅手段の入力段に直流帰還を施す
直流帰還手段とを備えて成ることを特徴とする電流検出
装置。2. A current detecting device for detecting a detected current by detecting a current flowing on an output side corresponding to a detected current flowing on an input side of a current transformer, wherein the current detecting device is connected to an output of the current transformer. Current input type differential amplifying means comprising a differential amplifier which produces an output proportional to the current flowing through the input terminal; and a direct current from an output stage of the current input type differential amplifying means to an input stage of the current input type differential amplifying means. A current detection device comprising: DC feedback means for performing feedback.
て出力側に流れる電流を検出することにより前記検出電
流を検出する電流検出装置において、 前記変流器出力の一方の端子に接続された第１の電流入
力増幅器と、前記変流器出力の他方の端子に接続された
第２の電流入力増幅器とを備え、前記一方の端子と前記
第１の電流入力増幅器との接続点に前記第２の電流入力
増幅器の出力を注入することにより、浮遊容量を介して
前記変流器に誘起した雑音成分を打ち消すことを特徴と
する電流検出装置。3. A current detecting device for detecting a detected current by detecting a current flowing on an output side corresponding to a detected current flowing on an input side of a current transformer, wherein one terminal of an output of the current transformer is provided. A first current input amplifier connected thereto, and a second current input amplifier connected to the other terminal of the current transformer output, and a connection point between the one terminal and the first current input amplifier. A current detection device for injecting an output of the second current input amplifier to cancel a noise component induced in the current transformer via a stray capacitance.
第１の電流入力増幅器の入力へ直流帰還を施す直流帰還
手段を有する請求項３に記載の電流検出装置。4. The current detecting device according to claim 3, further comprising DC feedback means for performing DC feedback from an output of said first current input amplifier to an input of said first current input amplifier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP09459497A JP3999303B2 (en) | 1997-03-28 | 1997-03-28 | Current detector |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP09459497A JP3999303B2 (en) | 1997-03-28 | 1997-03-28 | Current detector |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10274665A true JPH10274665A (en) | 1998-10-13 |
| JP3999303B2 JP3999303B2 (en) | 2007-10-31 |
Family
ID=14114611
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP09459497A Expired - Lifetime JP3999303B2 (en) | 1997-03-28 | 1997-03-28 | Current detector |
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| Country | Link |
|---|---|
| JP (1) | JP3999303B2 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2012049955A (en) * | 2010-08-30 | 2012-03-08 | Hioki Ee Corp | Current/voltage conversion circuit and current detector |
| CN103605311A (en) * | 2013-12-06 | 2014-02-26 | 国电南京自动化股份有限公司 | Circuit for acquiring switching value by virtue of transformer flyback pulse shaping |
| RU2617858C1 (en) * | 2015-12-11 | 2017-04-28 | Евгений Иванович Рожнов | Electronic current transformer |
-
1997
- 1997-03-28 JP JP09459497A patent/JP3999303B2/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2012049955A (en) * | 2010-08-30 | 2012-03-08 | Hioki Ee Corp | Current/voltage conversion circuit and current detector |
| CN103605311A (en) * | 2013-12-06 | 2014-02-26 | 国电南京自动化股份有限公司 | Circuit for acquiring switching value by virtue of transformer flyback pulse shaping |
| RU2617858C1 (en) * | 2015-12-11 | 2017-04-28 | Евгений Иванович Рожнов | Electronic current transformer |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3999303B2 (en) | 2007-10-31 |
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