JPH01189567A - Direct-current detector - Google Patents

Abstract

PURPOSE:To enable the detection of a current with high accuracy, by a method wherein an alternating-current power supply generating a pulsating alternating-current voltage waveform having a quiescent period is used as an alternating-current power supply given to output windings of magnetic amplifiers of two sets. CONSTITUTION:An alternating-current power supply for two magnetic amplifiers 6 and 7 is supplied from a transformer 11 having insulated windings. A primary-winding voltage of this transformer 11 is supplied from a pulse voltage generator 12 which outputs an alternating-current voltage of a rectangular wave having a quiescent period. This alternating-current voltage makes a frequency low and the quiescent period in one cycle long unless cores of the amplifiers 6 and 7 are saturated. This quiescent period is a state wherein an ampere-turn of a current flowing through a primary conductor 1 is balanced with an ampere-turn due to a current flowing through a feed- back winding 2, so that an output be detected. Since an exciting current is fixed in this quiescent period, the exciting current of the amplifiers 6 and 7 is easy to cancel and therefore the effect thereof on the output is very small. By using this period as a measured current value accordingly, the execution of current measurement of high accuracy is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a high-speed, high-precision DC current detector that reduces the influence of the excitation current of an iron core and extremely reduces ripple voltage errors in detection.

[Conventional technology]

FIG. 4 shows a conventional DC current detector disclosed in, for example, Japanese Unexamined Patent Publication No. 55-60860. In the figure, there are 2&lI magnetic amplifiers (6) and (7) using four iron cores, and the circuit operation is as follows. Detected current■.

flows through the winding +11, and a current proportional to that flows through the output resistors (9) and aω of the magnetic amplifiers (6) and (7). The relationship between these input currents 1 and the output voltage e0 is as shown in FIGS. 5(a) and 5(b). The output voltages e1 and e2 are algebraically summed to become eo in FIG.
) and stops when the amperage of the current becomes equal to the winding +11. Therefore, this current is transferred to the output resistance (5
), the value is proportional to the detected current, and by converting it, the primary side current value can be measured correctly.

However, since an iron core is used, an excitation current is required, and its value is not preferable because it causes a ripple error in the detected value. This state indicates that no matter how high the average value detection accuracy is, the instantaneous value accuracy is poor.

[Problem to be solved by the invention]

As mentioned above, conventional DC current detectors generate ripple voltage due to the excitation current of the iron core, so when used as a feedback signal for a current control circuit as a highly constant and high-speed current detector, the response characteristics and accuracy may be affected. The problem was that it wasn't enough.

This invention was made to solve the above-mentioned problems, and aims to obtain a high-speed, high-precision current detector by reducing the influence of the exciting current of the iron core and eliminating the influence of the detected ripple voltage. purpose.

[Means to solve the problem]

The DC current detector according to the present invention uses two sets of magnetic amplifiers, and the applied waveform of the AC power is made into a pulse shape having a rest period.

[For production]

In this invention, the current is detected during the rest period when no voltage is applied, so there is no change in the magnetic flux, and therefore the excitation current is also constant, so the influence of the excitation current of the two sets of magnetic amplifiers is easily canceled out, and the excitation current The effect on the output will be very small.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

The AC power source for each of the two magnetic amplifiers (6) and (7) shown in FIG. 1 is supplied from a transformer 0υ having an insulated winding. The primary winding voltage of the transformer Oυ is supplied from a pulse voltage generator (2) which outputs a rectangular wave AC voltage having a rest period (tz tz) as shown in FIG. 3 <a>. The alternating voltage has a low frequency and a large rest period within a cycle, unless the core of the magnetic amplifier is saturated. In other words, T1<<T. The hysteresis ring within the iron core α1 in such an applied voltage waveform is
As shown in the figure. In Fig. 2, the rectangular voltage E is D+tz) from point a (point t1 in time) of the saturated half cycle of the magnetic amplifier.
When applied between Lt and t3, the magnetic flux passes through point b and is rapidly reset to the 0 point. Since no voltage is applied between Lt and t3, no fluctuation in magnetic flux occurs. During this period, the primary conductor (1)
The ampere-turn of the current flowing through the feedback winding (2) and the ampere-turn of the current flowing through the feedback winding (2) are balanced, and the output is detected.

Since the excitation current is constant during this period, the excitation currents of the two magnetic amplifiers are easily canceled out and the influence on the output is extremely small. Therefore, by using this period as a current measurement value, highly accurate current detection becomes possible. time 1
．． -1. Since the opposite voltage -E is applied between them, the magnetic flux is d
It passes through the point and becomes saturated at point a. In the next half cycle of this period, the other magnetic amplifier is released from saturation and becomes operational.

FIG. 3(b) shows the value of magnetic flux within the iron core over time, and shows the value of the magnetic flux in the iron core during the rest period 1. -1. This indicates that there is no change between (-) and that it is constant.

In addition, period 1. -1. During this period, the magnetic flux changes and the excitation current also changes, which is a period in which ripple voltage is likely to be detected. However, there is no change in the fact that during this period, the primary winding current and the current flowing into the feedback winding can be measured equally in ampere-turns.

The applied voltage waveform in the present invention is not particularly limited to a rectangular wave, and any waveform may be used as long as it can provide a large rest period.

〔Effect of the invention〕

As described above, according to the present invention, the current detector is driven by a power supply voltage having a rest period, and the value is measured within the rest period, so that high-speed, high-precision DC current detection is less affected by the excitation current of the iron core. There is an effect that the vessel can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a DC current detector according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of the hysteresis ring of the iron core in the electric circuit of FIG. 1, and FIG. A waveform diagram showing changes in the voltage waveform of the generator and magnetic flux density in the iron core, Figure 4 is an electric circuit diagram of a conventional DC current detector, and Figure 5 is a diagram for explaining the operation of the electric circuit in Figure 4. It is a characteristic diagram. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa/j:, Kumi~・ Figure 2 Figure 3 t7 (z t3t4 Figure 4 Figure 5 Procedural amendment (voluntary) Showa year, month, day 2, name of the invention DC current detector 3, Relationship with the case of the person making the amendment Patent Applicant Address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Moriya Shiki 4, Agent 5 Subject of amendment (1) Figures & Contents of amendment (Figure 5 of 12 drawings is corrected as shown in the attached sheet. 7. List of attached documents (υ Corrected drawings (Figure 5) 1 or more copies Figure 5 (C)

Claims (1)

[Claims] Two sets of magnetic amplifiers each having two magnetic bodies magnetically coupled to a conductor through which a current to be detected flows are used, and each magnetic body has a bias winding that applies a bias and a feedback winding. Lines and,
A feedback amplifier amplifies the difference signal between the two outputs obtained from the output windings of the two sets of magnetic amplifiers to provide a feedback signal to the feedback winding, and this feedback signal is used to detect the detected signal. In a current detector that uses this feedback signal as a current detection value so as to cancel out the magnetomotive force caused by the current, the AC power supplied to the output windings of the two sets of magnetic amplifiers is
A DC current detector characterized by using an AC power source that generates a pulse-like AC voltage waveform having a rest period.