JP6718355B2 - Isolated transmission device - Google Patents

Description

The present invention relates to an insulated transmission device that insulatedly transmits an input signal.

Insulation voltage measurement is one of the methods to ensure the safety when high-voltage equipment is used as the voltage measurement target. By performing the insulation voltage measurement, it becomes possible to safely handle voltages having different ground potentials between the measurement target and the measuring device. That is, the safety of the grounded measuring instrument side is maintained even if the measurement target that is in an insulating state (floating) with respect to the earth ground is at a high voltage level. Further, in the insulation voltage measurement, the noise caused by the ground impedance can be removed by cutting the ground loop between the measurement target and the measuring instrument.

For insulation voltage measurement, a measuring instrument with an insulation circuit is widely used, but even with a measuring instrument that does not have an insulation circuit, use an isolation amplifier with an insulation circuit to measure the insulation voltage. You can

Typical methods of insulating circuits include an optical coupling method that uses a photocoupler, a magnetic coupling method that uses a transformer, and a capacitive coupling method that uses a capacitor. Isolation circuits are also used.

FIG. 7: is a figure which shows the structural example of the conventional insulated transmission apparatus 500 using the insulation circuit of a composite type transmission system. The insulated transmission device 500 is a device that performs insulated transmission from the floating side circuit 510 to the ground side circuit 520. The insulated transmission device 500 uses a composite transmission type insulation circuit in which a transformer 540 and a photocoupler 530 are combined, and the insulated transmission path is divided according to the frequency band of the transmission signal.

That is, the low frequency signal including direct current is insulated and transmitted by the photocoupler 530, and the middle and high frequency signals are insulated and transmitted by the high frequency transformer 540 connected through the capacitor C.

The analog signals transmitted to the ground side circuit 520 through the respective insulated transmission paths are added in the ground side circuit 520 and output. At this time, various parameters are adjusted so that the frequency characteristic of the crossover band between the low-frequency signal and the mid-high frequency signal becomes flat.

In the insulated transmission device 500, since the insulated transmission is performed by the analog signal, the probe device for guiding the input signal from the measurement target can be miniaturized without requiring electric power.

JP, 08-256027, A

In recent years, as devices have become faster and have higher withstand voltage, an insulated transmission device that is compatible with a wide band and a wide voltage range from low voltage to high voltage has been desired. Here, in the voltage range supported by the insulated transmission device 500, the maximum applied voltage of the photocoupler 530, which is an insulated transmission path for low-frequency signals, is about 1 kV, so the voltage range on the high voltage side is the range of the photocoupler 530. It depends on the pressure resistance.

For this reason, it is difficult for the insulated transmission device using the photocoupler 530 to support a wider voltage range. Therefore, an object of the present invention is to widen the corresponding voltage range of the insulated transmission device.

In order to solve the above problems, an insulated transmission device of the present invention is an insulated transmission device that performs insulated transmission of an input signal, and has a flux gate circuit, and detects a current flowing through a primary conductor of the flux gate circuit. A low-range insulated transmission circuit that performs low-frequency isolated transmission including the direct current of the input signal, a transformer that performs medium-high range insulated transmission of the input signal, and a signal transmitted by the low-range insulated transmission circuit and the transformer. And an adder circuit for adding the signal transmitted by the above method.
Here, a high-pass filter for separating the input signal into a low-frequency signal guided to the low-frequency insulated transmission circuit and a mid-high frequency signal guided to the transformer can be provided.
The adder circuit may differentially amplify the signal transmitted by the transformer and add the signals transmitted by the low frequency isolated transmission circuit.
Further, the transformer may have a center tap.

According to the present invention, the corresponding voltage range of the insulated transmission device can be expanded.

It is a figure which shows the structure of the insulated transmission apparatus which concerns on this embodiment. It is a figure which shows a floating side circuit. It is a figure which shows the low frequency insulated transmission circuit containing the flux gate circuit. It is a figure for demonstrating the core of a flux gate circuit. It is a figure for explaining single transmission and differential transmission. It is a figure for explaining a transformer. It is a figure which shows the structural example of the conventional insulated transmission apparatus using the insulation circuit of a composite type transmission system.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an isolated transmission device 100 according to the present embodiment. As shown in the figure, the insulated transmission device 100 is a device that performs insulated transmission of an analog signal from the floating side circuit 110 to the ground side circuit 120. The insulated transmission device 100 can be used, for example, as a measuring device for performing insulation measurement, an insulation amplifier, or the like.

The insulated transmission device 100 uses a composite transmission type insulation circuit in which the transformer 140 and the flux gate circuit 150 are combined, and the insulated transmission path is divided according to the frequency band of the transmission signal.

That is, a low frequency signal from DC to several kHz is insulated and transmitted by the flux gate circuit 150, and a middle and high frequency signal of several kHz to several hundred MHz is insulated and transmitted by the high frequency transformer 140.

As described above, in the present embodiment, the flux gate circuit 150 that is normally used as a magnetic sensor or a current sensor is used as an insulating transmission circuit for low-frequency signals. Since the flux gate circuit 150 is superior in withstand voltage performance to the photocoupler, it is possible to widen the applicable voltage range of the insulated transmission device.

FIG. 2 is a diagram showing the floating side circuit 110. As shown in FIG. 1 and FIG. 2, a signal in which the DC component is cut by the high-pass filter 111 is input to the transformer 140 that insulation-transmits the middle-high band signal. This prevents a direct current component from flowing into the transformer 140 and hindering stable operation. However, the DC component may be cut using a capacitor as in the conventional case.

The high-pass filter 111 has a circuit configuration in which the output of a differential amplifier circuit that inputs a transmission signal is fed back by an integrating circuit. Both the differential amplifier circuit and the integration circuit have a basic configuration using operational amplifiers. However, the high pass filter 111 may have another circuit configuration.

Then, the low-pass signal that does not pass through the high-pass filter 111 is converted into a current by the shunt resistor Rs1 and is made to flow through the primary conductor of the flux gate circuit 150, and the primary side current is obtained. A block including the flux gate circuit 150 for performing low frequency insulated transmission is referred to as a low frequency insulated transmission circuit 130.

FIG. 3 is a diagram showing a low frequency isolated transmission circuit 130 including a flux gate circuit 150. The flux gate circuit 150 generates a current corresponding to the primary side current flowing through the primary conductor, and the detection resistor Rs2 detects the current value. Since the primary conductor and the detection resistor Rs2 are insulated, they can be used for insulated transmission. However, since the high frequency characteristics of the flux gate circuit 150 are not sufficient, the flux gate circuit 150 is used for low frequency insulated transmission, and the medium and high frequency side insulated transmission is a composite type transmission system using the high frequency transformer 140.

Although various methods have been proposed for the fluxgate circuit, in the present embodiment, a band close to direct current is modulated by an exciting coil at fr>100 kH to extract a signal, and a band higher than that is used. , It is taken out by operating the current transformer with the detection coil. Then, the current obtained by adding the two signals is converted into a voltage by the detection resistor Rs2 and detected.

The pulse applied to the exciting coil causes a saturation operation of the core, so that a certain amount of current is required. The low-pass filter LPF is provided in both the floating-side circuit 110 and the ground-side circuit 120 so as not to affect the mid-high range signal even if this current flows into the detection coil or the primary conductor by capacitive coupling through the core. .. The cutoff frequency of the low-pass filter LPF is set to a value that can cut the fundamental frequency of the pulse signal applied to the exciting coil and can pass the frequency component to be transmitted by the low-frequency insulated transmission circuit 130 without being attenuated.

As shown in FIG. 4, the core of the flux gate circuit 150 is formed by winding an exciting coil for detecting a DC component on a magnetic body and a feedback coil (detection coil) for zero flux. There is. From the viewpoint of pressure resistance, it is preferable to use a three-layer insulated wire which is a high-insulation wire, and to wrap an insulating tape (polyester) to further increase the pressure resistance. It is also preferable to use a three-layer insulated wire for the primary conductor that carries the primary side current.

The core is a magnetic substance and can be regarded as a metal, but it can be regarded as a non-metal by winding a magnetic substance, a three-layer insulated wire, and an insulating tape. This makes it possible to view the total distance from the soldered portion of the primary conductor to the soldered portion on the ground side as a creepage distance. Further, by reducing the number of turns of the primary conductor, it is possible to suppress the coupling capacitance between the floating side and the ground side, which leads to improvement of IMRR characteristics in the high frequency range.

In the isolated transmission device 100, the differential amplifier circuit 160 is used on the output side of the transformer 140. In the conventional single transmission, as shown in FIG. 5A, the common mode voltage on the floating side is transmitted to the ground side through the transformer, and the reference potential (GND) of the operational amplifier that receives a signal on the ground side is changed, This causes the operational amplifier to shake and is superimposed on the transmitted signal. As a result, the common mode is converted to the normal mode and affects the output signal.

On the other hand, in the case of differential transmission, as shown in FIG. 5B, the common mode voltage can be separated from the reference potential (GND) of the operational amplifier, and the common mode voltage transmitted from the floating side is output. It is possible to suppress the influence on the signal.

Note that, as shown in FIG. 1, the transformer 140 has a single side on the primary side and a differential on the secondary side, and uses a center tap on the secondary side. The center tap plays a role of releasing a large-amplitude noise component jumping in from the primary side to the ground, and thus prevents the operational amplifier arranged in the subsequent stage from being saturated. At this time, it is desirable that the resistors used in the differential amplifier circuit 160 have high relative accuracy.

The transformer 140 is basically an AC transformer in which a coil is wound around a magnetic body as shown in FIG. The core itself is a magnetic body like the core of the flux gate circuit 150 and can be regarded as a metal. When there is a metal in the middle, the total distance from the floating side/ground side to the metal is calculated as the creepage distance.

By using a three-layer insulated wire and adjusting the number of windings according to the mid-high range where you want to pass the creepage/space distance, it is possible to easily cope with the distance required for high-voltage floating voltage. Become. It is possible to reduce the number of turns by using a core with the highest initial magnetic permeability as the core, and as a result, it is possible to suppress the coupling capacitance between the floating side and the ground side, which leads to improved IMRR characteristics up to high frequencies. ..

Furthermore, by providing an insulating coating on the magnetic body itself, it becomes possible to further improve the withstand voltage performance similarly to the core of the flux gate circuit 150, and it is possible to further secure safety.

100... Insulation transmission device, 110... Floating side circuit, 111... High-pass filter, 120... Ground side circuit, 130... Low frequency isolation transmission circuit, 140... Transformer, 150... Flux gate circuit, 160... Differential amplification circuit

Claims (4)

An isolated transmission device that performs isolated transmission of an input signal,
Has a fluxgate circuit with the primary conductor and the excitation coil and the detection coil, performs insulation transmission of low frequency including DC of the input signal by detecting a current flowing through the primary conductor of the fluxgate circuit Low frequency isolated transmission circuit,
A transformer that performs isolated transmission of the input signal in the middle and high frequencies,
An adder circuit for adding the signal transmitted by the low frequency isolated transmission circuit and the signal transmitted by the transformer,
Equipped with
An insulated transmission device , wherein a three-layer insulated wire is used for the primary conductor, the exciting coil, and the detection coil . The insulated transmission device according to claim 1, further comprising a high-pass filter that separates the input signal into a low-frequency signal that is guided to the low-frequency insulated transmission circuit and a mid-high frequency signal that is guided to the transformer. 3. The insulated transmission device according to claim 1, wherein the adder circuit differentially amplifies the signal transmitted by the transformer and adds the signals transmitted by the low frequency insulated transmission circuit. The insulated transmission device according to claim 1, wherein the transformer has a center tap.