JP2017009502A - Current detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detection circuit that has high insulating performance between the detection circuit and a point to be measured, is high in sensitivity and compact, and can be made compact.SOLUTION: A current detection circuit 100 consists of a transformer T1 comprising a magnetic core of high-magnetic-permeability material, an AC current generation circuit 110 connected to the transformer T1, and a determination circuit 120 determining an output voltage of an operational amplifier U1 that the AC current generation circuit 110 comprises. The determination circuit 120 consists of a window comparator 121 and a counting circuit 122. When a current flows to primary winding of the transformer T1, a secondary winding current value until the magnetic core of the transformer T1 reaches saturation magnetic flux density with a secondary winding current varies in proportion to the direction and level of the current from that when no current flows to the primary winding. The shift quantity thereof is proportional to the primary winding current, so a numeral proportional to the primary winding current can be obtained through the window comparator 121 and counting circuit 122.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a current detection circuit that detects a ground fault of a DC high voltage circuit such as a photovoltaic power generation or a storage battery system.

  In photovoltaic power generation and stationary storage battery systems, the power generation unit and the inverter device are often connected with a voltage of several hundred volts or more in order to increase the power generation efficiency. Therefore, for the purpose of ensuring safety, protection against electric shock is achieved, for example, power is cut off when a ground fault current is detected at a predetermined value or more.

  In order to detect a ground fault current in a photovoltaic power generation or a stationary storage battery system, since a photovoltaic power generation panel or storage battery is a direct current power source, a current detector that can be measured from direct current is required (see Patent Document 1). . In addition, since the detection lower limit value in the ground fault current detection is about several hundred μA to several mA, the DC drift characteristic is required to be very small.

  Furthermore, in the current detector, the detection unit and the operation unit are often configured on the same common line. In this case, the detection unit and the measurement point are isolated from each other for convenience of human operation and communication with other devices. It is necessary to be. Further, in order not to increase the circuit scale, it is preferable that the insulation point is performed in the immediate vicinity of the measurement point.

JP 2006-187150 A

  However, in the past, a current sensor using a Hall element has been used for detecting the ground fault current. However, since the sensitivity is low, the ground fault current detection line must be wound for several to several tens of turns. There was a problem that the DC drift was large and the price was high.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a current having high insulation performance between a detection circuit and a measurement point, high sensitivity, low cost, and miniaturization. It is to provide a detection circuit.

  In order to solve the above-described problems, the present invention provides a current detection circuit, a transformer having a primary winding and a secondary winding having a magnetic material as a magnetic core, and the magnetic core connected to the secondary winding. An AC current generation circuit for flowing an AC current having a peak value greater than or equal to a magnetic saturation current to the secondary winding, and a determination circuit for determining a change in the peak position of the voltage waveform of the secondary winding, The amount of current flowing through the primary winding is determined from the determination result of the change in the peak position of the voltage waveform.

  According to a second aspect of the present invention, in the current detection circuit according to the first aspect, the alternating current is a triangular wave current.

  According to a third aspect of the present invention, in the current detection circuit according to the first aspect, the primary winding is one or two turns.

  According to a fourth aspect of the present invention, in the current detection circuit according to any one of the first to third aspects, the magnetic core is an amorphous permalloy.

  According to a fifth aspect of the present invention, in the current detection circuit according to any one of the first to fourth aspects, the determination circuit includes a window comparator and a counting circuit, and a positive voltage peak detected by the window comparator is detected. The amount of current flowing in the primary winding is determined by measuring the interval from the negative voltage peak with the counting circuit.

  According to a sixth aspect of the present invention, in the current detection circuit according to any one of the first to fourth aspects, the determination circuit includes an A / D converter and a processor.

  The present invention has the effect of increasing the sensitivity of current detection, reducing the price, and reducing the size of the current detector. Further, it is possible to easily reduce the DC drift.

It is a figure which shows the structure of the current detection circuit which concerns on Embodiment 1 of this invention. It is a figure which shows the magnetic saturation characteristic of a high magnetic permeability material. It is a figure which shows the voltage induced by the secondary winding of the trans | transformer T1 when operating a current detection circuit in one Embodiment of this invention. It is a figure which shows the voltage induced by the secondary winding of the transformer T1 when an electric current flows into the primary winding of the transformer T1 in one Embodiment of this invention. It is a figure which shows the structure of the current detection circuit which concerns on another embodiment of this invention.

  The present invention uses a magnetic saturation characteristic of a magnetic material to detect DC current detection that requires high sensitivity and excellent stability and insulation performance, such as ground fault detection of a DC high voltage circuit such as a photovoltaic power generation system or a storage battery system. And it is realized simply. Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 shows a configuration of a current detection circuit according to an embodiment of the present invention. The current detection circuit 100 according to the first embodiment includes a transformer T1 having a magnetic core made of a high permeability material, an AC current generation circuit 110 connected to the transformer T1, and an output voltage of an operational amplifier U1 provided in the AC current generation circuit 110. And a determination circuit 120 for determining whether or not. The determination circuit 120 includes a window comparator 121 and a counting circuit 122.

  In the transformer T1, the primary winding has about 1 or 2 turns, whereas the secondary winding can have about 20 turns.

  The alternating current generation circuit 110 includes a triangular wave voltage source 111, a resistor R1, and an operational amplifier U1. The secondary winding of the transformer T1 is connected to a feedback path between the output of the operational amplifier U1 and the negative input, and the positive input of the operational amplifier U1 is set to the ground potential. The frequency of the triangular wave voltage source 111 may be about 1 kHz. In the embodiment shown in FIG. 1, the triangular wave voltage source 111 is used. However, the voltage generated by the voltage source is not limited to the triangular wave and may be a sine wave or the like.

Here, when a triangular wave voltage v is added to the negative input of the operational amplifier U1 through the resistor R1, the current I flowing through the secondary winding of the transformer T1 is set to a sufficiently large value of the open loop gain of the operational amplifier U1.
I = v / R1
Thus, a triangular wave current proportional to the voltage v is obtained. The resistor R1 is set so that the peak value of the triangular wave current I is higher than the saturation magnetic flux density of the magnetic core of the transformer T1. Thereby, even if a magnetic core is magnetized, it can degauss.

FIG. 2 shows the magnetic saturation characteristics of the high permeability material. As the magnetic core of the transformer T1, as shown in FIG. 2, a magnetic material having a steep magnetic saturation characteristic and a small hysteresis, for example, an amorphous permalloy having a relative permeability of about 1 × 10 ⁴ can be used.

In general, the permeability μ is the slope of the BH curve, that is, μ = B / H.
It is represented by As can be seen from this curve, the magnetic permeability is very high until the magnetic saturation occurs, and when the saturation magnetic flux density is reached, the slope suddenly approaches zero.

  Therefore, when the magnetic core of the transformer T1 reaches the saturation magnetic flux density due to the secondary winding current of the transformer T1, the secondary winding inductance becomes very small, and when the magnetic core is in the non-saturated state, the inductance becomes large.

  FIG. 3 shows the voltage induced in the secondary winding of the transformer T1 when the current detection circuit is operated in one embodiment of the present invention. The voltage induced in the secondary winding, that is, the output voltage (2) of the operational amplifier U1, changes with a large peak as shown in FIG. 3 according to the inductance change of the secondary winding of the transformer T1.

  Here, when a current flows through the primary winding of the transformer T1, the secondary winding current value until the magnetic core of the transformer T1 reaches the saturation magnetic flux density due to the secondary winding current is proportional to the direction and magnitude thereof. Changes when no current is flowing through the primary winding. FIG. 4 shows a voltage induced in the secondary winding of the transformer T1 when a current flows through the primary winding. For this reason, when the primary winding current flows in the positive direction, the peak position of the U1 output voltage (2) is shifted as shown by the dashed line, and when the primary winding current flows in the negative direction, the waveform shown by the dotted line is obtained. Shift to. When the frequency is about 1 kHz, the shift amount is several tens percent between the positive voltage peak and the negative voltage peak, and a change of about 0.1 to 0.2 ms occurs.

  Since this shift amount is a value proportional to the primary winding current, a numerical value proportional to the primary winding current can be obtained by the window comparator 121 and the counting circuit 122 as shown in FIG. That is, the time interval between the positive voltage peak and the negative voltage peak is measured by the counting circuit 122, so that the primary corresponding to the time interval is obtained from the correspondence relationship between the primary winding current value and the time interval obtained in advance. The winding current value can be determined. Of course, as shown in FIG. 5, it is also possible to determine the amount of change in the waveform using the A / D converter 221 and the processor 222 as the determination circuit 220 and obtain the primary winding current value.

  As described above, according to the present invention, an alternating triangular wave current exceeding the magnetic saturation of the transformer core positively and negatively flows, so that the magnetic core is hard to be magnetized, and offset drift due to magnetism is less likely to occur than a current sensor using a Hall element or the like. can do. Moreover, since the magnetic saturation point of the magnetic core is stable with respect to temperature, the temperature stability is also high.

  Further, the present invention can obtain a large and steep detection voltage when transitioning between a magnetic saturation point and a non-saturation point by using amorphous permalloy having a high magnetic permeability and steep magnetic saturation characteristics as a magnetic core material. Thereby, since a pulse interval proportional to the primary circuit current can be obtained with a simple circuit such as a window comparator, a small and low-cost current detection circuit can be provided.

110, 210 AC current generation circuit 111 Voltage source 120, 220 Determination circuit 121 Count circuit 122 Window comparator 221 A / D converter 222 Processor U1 Operational amplifier

Claims (6)

A transformer having a primary winding and a secondary winding with a magnetic material as a magnetic core;
An alternating current generating circuit that is connected to the secondary winding and causes an alternating current having a peak value equal to or higher than a current at which the magnetic core is magnetically saturated to flow to the secondary winding;
A determination circuit for determining a change in the peak position of the voltage waveform of the secondary winding;
And a current detection circuit for determining an amount of current flowing through the primary winding from a determination result of a change in a peak position of the voltage waveform.   The current detection circuit according to claim 1, wherein the alternating current is a triangular wave current.   The current detection circuit according to claim 1, wherein the primary winding is one or two turns.   The current detection circuit according to claim 1, wherein the magnetic core is an amorphous permalloy.   The determination circuit includes a window comparator and a counting circuit, and the current flowing in the primary winding is measured by measuring the interval between the positive voltage peak and the negative voltage peak detected by the window comparator with the counting circuit. The current detection circuit according to claim 1, wherein the amount is determined.   The current detection circuit according to claim 1, wherein the determination circuit includes an A / D converter and a processor.