JP7720179B2 - Current sensors and watt-hour meters - Google Patents

Description

The present invention relates to a current sensor and watt-hour meter that are small, highly sensitive, and less susceptible to external magnetic fields.

Current sensors that have traditionally been used include current transformers (CTs), sensors that place a magnetic detection element such as a Hall element in the gap of a magnetic core, and sensors that place a wound coil or an element with a coil pattern formed on a dielectric substrate in the gap of a magnetic core. Because these methods use magnetic materials, they tend to be large in size to prevent saturation at large currents, which increases costs.

There are also methods that use only a coil pattern formed on a printed circuit board without using a magnetic core. These methods have the advantage of being small and inexpensive, as they are constructed using only a coil pattern formed on a printed circuit board.

In Patent Document 1, to detect the magnetic flux generated by the measurement current, a pair of first coils C1, each formed with a multi-turn conductive pattern on both sides of a circuit board and shaped symmetrically on the front and back, and a second coil C2, arranged symmetrically to the first coil with respect to the position where the measurement wiring is placed, are used. By arranging the coils symmetrically above and below the position of the measurement wiring, the coils arranged symmetrically above and below the measurement wiring detect the magnetic flux around the measurement wiring, and the current can be measured by bringing the coil close to the measurement target without cutting or changing the circuit wiring.

Patent No. 5846421

The current sensor in Patent Document 1 is designed to measure relatively high-frequency signals with a pulse width of approximately 10 μs. For example, if this configuration is applied to a current sensor installed in a power meter or the like, the low frequency of approximately 50 Hz to 60 Hz can result in insufficient current detection sensitivity. One solution to this problem is to increase the coil area and the number of coil turns, but this creates the problem of the sensor becoming larger in order to achieve sufficient sensitivity. Another method is to use a multi-layer board rather than a double-sided board as in Patent Document 1 to increase the number of coil turns, but this can create problems such as increased susceptibility to external noise (external magnetic fields) depending on the connection positions of the first and second coils and the connection positions of each layer of the first and second coils.

The present invention was made in consideration of the above, and aims to provide a current sensor and watt-hour meter that are small, highly sensitive, and less susceptible to external magnetic fields.

To solve the above-mentioned problems and achieve the object, the present invention provides a current sensor that detects a magnetic field formed around a current bar through which a current flows and detects a current signal flowing through the current bar, wherein a first coil and a second coil that detect the magnetic field are formed on a multilayer printed circuit board, one end of the first coil and one end of the second coil are connected by a first via that connects the front and back surfaces of the multilayer printed circuit board, one of the other ends of the first coil or the second coil is connected to an external connection terminal within the same plane, and the other is connected to an external connection terminal via a second via that connects the front and back surfaces of the multilayer printed circuit board, the first via and the second via are located on different sides of a central plane that passes through the central axes of the first coil and the second coil, and a first interlayer connection via that is located on the outer periphery of the first coil among the interlayer connection vias that connect the layers of the first coil and a second interlayer connection via that is located on the outer periphery of the second coil among the interlayer connection vias that connect the layers of the second coil are located on different sides of the central plane.

Furthermore, in the above invention, the present invention is characterized in that the multilayer printed circuit board is composed of four or more layers, and a coil pattern is formed on each layer.

Furthermore, in the above invention, the present invention is characterized in that the first coil and the second coil are connected in series so as to reinforce the induced voltages generated by the magnetic field generated by the current flowing through the current bar.

The present invention is also characterized in that the amount of power flowing through the current bar is calculated based on the current signal detected by the current sensor and the voltage signal detected by the voltage sensor described in any one of the above inventions.

According to the present invention, by increasing the number of turns in a coil pattern formed on a multilayer printed circuit board, it is possible to measure commercial frequency currents with high sensitivity in a compact device, and by connecting two coils in a way that cancels out the effects of external noise (external magnetic fields), it is possible to provide a high-precision current sensor that is less susceptible to such effects.

FIG. 1 is a diagram showing a schematic configuration of a current sensor according to an embodiment of the present invention. FIG. 2 is a plan view of the current sensor. FIG. 3 is a diagram showing the pattern configuration of each layer of the current sensor. FIG. 4 is a diagram showing the results of analyzing the influence of an external magnetic field on this embodiment and other connection examples A and B. FIG. 5 is an explanatory diagram illustrating the influence of an external magnetic field in the Z direction on this embodiment and another connection example A. FIG. 6 is an explanatory diagram illustrating the influence of an external magnetic field in the X direction in this embodiment and in connection example B. In FIG. FIG. 7 is a block diagram showing an example of a watt-hour meter using the current sensor shown in the embodiment. FIG. 8 is a vector diagram between three-phase currents and three-phase voltages.

The following describes an embodiment of the present invention with reference to the accompanying drawings.

Figure 1 shows the general configuration of a current sensor 3 according to an embodiment of the present invention, with Figure 1(a) showing a side view of the current sensor 3 and Figure 1(b) showing a perspective view of the current sensor 3. As shown in Figure 1, the current sensor 3 is placed near a current bar 1 through which the current to be measured flows. The current sensor 3 has a first coil 2a and a second coil 2b, which are pattern coils, placed on a multi-layer printed circuit board. The first coil 2a and the second coil 2b have a four-layer structure of the same size and are positioned at equal positions on the left and right of the current bar 1.

Figure 2 is a plan view of the current sensor 3. Figure 3 is a diagram showing the pattern configuration of each layer of the current sensor 3. As shown in Figure 2, external connection terminals 22a and 22b are terminals for connecting to a signal processing circuit (not shown).

The first coil 2a and second coil 2b detect the magnetic field generated by the current I flowing through the current bar 1, and generate an induced voltage according to the current and frequency. The first coil 2a and second coil 2b are positioned at equal left and right positions across the current bar 1, and detect the magnetic flux Φ of different directions generated by the current I. The first coil 2a and second coil 2b are connected in series so that the induced voltages generated in each coil are added together. This induced voltage is then integrated by a signal processing circuit to output a detection signal proportional to the current I.

The larger the coil area and the more turns, the greater the induced voltage output. Therefore, the induced voltage generated is small at low frequencies, such as commercial frequencies of 50 Hz to 60 Hz. Therefore, sensitivity can be ensured by increasing the coil area or the number of turns. Increasing the coil area results in an increase in the size of the current sensor, so it is preferable to increase the number of turns within a limited area. However, since the wiring spacing and conductor width of coil patterns formed on printed circuit boards are subject to manufacturing limits, it is desirable to increase the number of layers on the printed circuit board to ensure a greater number of turns and ensure detection sensitivity. For this reason, in this embodiment, if a coil pattern is formed with four layers, an area of approximately 10 mm square, and a wiring conductor width and spacing of 0.1 mm, an induced voltage of approximately 0.1 mV/A (50 Hz) can be obtained, calculated as the sum of the two coils.

As shown in Figure 3, the four layers L1, L2, L3, and L4 are the front surface, first inner layer, second inner layer, and back surface, respectively. The first coil 2a and second coil 2b each have a coil pattern of the same area arranged on each layer L1, L2, L3, and L4. The coil patterns are formed in the same winding direction so that the induced voltages of each layer L1, L2, L3, and L4 are added together.

The first coil 2a is connected to the external connection terminal 22a via end P0 of the first coil through vias a1, b1, c1, and d1 in that order. Here, the lower position of via d1 on layer L4 is end P1 of the first coil 2a. Via d1 on layer L1 is connected to end P2 of the second coil 2b on layer L1, and the second coil 2b is connected to the external connection terminal 22b through vias a2, b2, c2, and d2 in that order. Here, the lower position of via d2 on layer L4 is end P3 of the second coil 2b. Then, by connecting end P1 of the first coil 2a and end P2 of the second coil 2b, the induced voltage of the first coil 2a and the induced voltage of the second coil 2b become additive.

Vias a1 and c1 are arranged on the central axis C10 of the first coil 2a, and vias b1 and d1 are arranged on the outer periphery of the first coil 2a. Similarly, vias a2 and c2 are arranged on the central axis C11 of the second coil 2b, and vias b2 and d2 are arranged on the outer periphery of the second coil 2b. Vias a1, c1, and b1 are interlayer connection vias for the first coil 2a, and vias a2, c2, and b2 are interlayer connection vias for the second coil 2b. Via d1 connects end P1 of the first coil 2a to end P2 of the second coil 2b. Via d2 connects end P3 of the second coil 2b to the external connection terminal 22b.

That is, end P1 of the first coil 2a and end P2 of the second coil 2b are connected by via d1, which connects the front surface (layer L1) and back surface (layer L4) of the multilayer printed circuit board; the other end P0 of the first coil is connected to external connection terminal 22a on the front surface; and the other end P3 of the second coil 2b is connected to external connection terminal 22b via via d2, which connects the front surface and back surface of the multilayer printed circuit board. Vias d1 and d2 are located on different sides of a central plane LC, which passes through the central axis C10 of the first coil 2a and the central axis C11 of the second coil 2b.

Furthermore, of the interlayer connection vias connecting the layers of the first coil 2a, vias a1 and c1 pass near the central axis C10, and via b1 is located on the outer periphery of the first coil 2a. Similarly, of the interlayer connection vias connecting the layers of the second coil 2b, vias a2 and c2 pass near the central axis C11, and via b2 is located on the outer periphery of the second coil 2b. Vias b1 and via b2 are located on different sides of the central plane LC.

By using such inter-coil connections and via arrangements, the effects of external magnetic fields can be suppressed. Figure 4 shows the results of an analysis of the effects of external magnetic fields on this embodiment and other connection examples A and B. In other connection example A, vias d1 and d2 are eliminated, and the inter-coil connections are made directly on the front or back surface. Therefore, the first coil 2a and second coil 2b in other connection example A have the same winding direction. In addition, in other connection example B, vias b1 and d1 and vias b2 and d2 are arranged on the same side of the center plane LC.

The analysis results show that connection example A is affected by an external magnetic field in the Z direction, and connection example B is affected by an external magnetic field in the X direction, but in this embodiment, there is no effect from any external magnetic field.

As for the external magnetic field in the Z direction, as shown in Figures 5(a) and 5(b), in this embodiment, the direction of the induced current flowing from vias a1, b1, and c1 toward via d1 is different from the direction of the induced current flowing from vias a2, b2, and c2 toward via d2, and the connections are such that the currents flow in these directions cancel each other out, thereby canceling out the induced voltage. On the other hand, in another connection example A, as shown in Figures 5(c) and 5(d), the currents flowing in vias b1 and b2 are different and are connected so that the currents flow in these directions overlap, forming a loop R1 and causing an external magnetic field in the Z direction to be detected.

On the other hand, with regard to the external magnetic field in the X direction, as shown in Figures 6(a) to 6(c), in this embodiment, vias d1 and d2 are arranged on different sides of the central plane LC, so the current directions in loop R1 formed by vias a1, c1 and via d1, as viewed from the X direction, and loop R2 formed by vias a2, c2 and via d2 are different, resulting in the induced voltage being canceled out. In contrast, in other connection example B, as shown in Figures 6(d) to 6(f), vias d1 and d2' are arranged on the same side of the central plane LC, so the current directions in loop R3 formed by vias a1, c1 and via d1, as viewed from the X direction, are the same as those in loop R4 formed by vias a2, c2 and via d2', resulting in the detection of an induced voltage.

Note that while the above embodiment shows an example of a four-layer coil, this is not limiting and any even number of layers may be used.

<Power meter>
Fig. 7 is a block diagram showing an example of a watt-hour meter 200 using the current sensor described in the embodiment. This watt-hour meter 200 measures three-phase power between a power source SP and a load LD, and calculates the power using the two-wattmeter method. Fig. 8 shows a vector diagram of the three-phase currents IR, IS, and IT and the three-phase voltages VR, VS, and VT.

As shown in FIG. 7, the watt-hour meter 200 has current sensors 3a and 3b corresponding to the current sensor 3 described in the embodiment, voltage sensors 201a and 201b, a watt-hour calculation unit 202, and an output unit 203. Current sensor 3a detects the R-phase current signal. Current sensor 3b detects the T-phase current signal. Voltage sensor 201a detects the voltage signal between the R and S phases. Voltage sensor 201b detects the voltage signal between the T and S phases.

The power calculation unit 202 multiplies the current signal from current sensor 3a by the voltage signal from voltage sensor 201a to generate an instantaneous power signal, smooths this signal using a low-pass filter to determine the active power, and multiplies the current signal from current sensor 3b by the voltage signal from voltage sensor 201b to generate an instantaneous power signal, smooths this signal using a low-pass filter to determine the active power, and calculates the active power by adding up each active power as the power amount. The output unit 203 displays or outputs the calculated power amount externally.

The three-phase power P calculated using the two-wattmeter method is:
P=VRS・IR+VTS・IT
=(VR-VS)・IR+(VT-VS)・IT
=VR・IR+VS・(-IR-IT)+VT・IT
=VR・IR+VS・IS+VT・IT
This is the same as calculating the total power of each phase.

Furthermore, the components illustrated in the above embodiments are merely functional schematics and do not necessarily have to be physically configured as shown. In other words, the distribution and integration of each device and component is not limited to that shown, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various usage conditions, etc.

1 Current bar 2a First coil 2b Second coil 3, 3a, 3b Current sensor 22a, 22b External connection terminal 200 Watt-hour meter 201a, 201b Voltage sensor 202 Watt-hour calculation unit 203 Output unit a1, a2, b1, b2, c1, c2, d1, d2 Via C10, C11 Central axis I Current IR, IS, IT Three-phase current L1, L2, L3, L4 Layer LC Central plane LD Load P Three-phase power P0 to P3 End R1 to R4 Loop SP Power supply VR, VS, VT Three-phase voltage Φ Magnetic flux

Claims (4)

A current sensor that detects a magnetic field formed around a current bar through which a current flows and detects a current signal flowing through the current bar,
a first coil and a second coil for detecting a magnetic field are formed on a multilayer printed circuit board having a coil pattern formed on each layer ;
one end of the first coil and one end of the second coil are connected by a first via that connects the front and back surfaces of the multilayer printed circuit board, one of the other end of the first coil or the other end of the second coil is connected to an external connection terminal within the same plane, and the other is connected to an external connection terminal through a second via that connects the front and back surfaces of the multilayer printed circuit board, the first via and the second via are arranged on different sides of a central plane that passes through a central axis of the first coil and a central axis of the second coil,
A current sensor characterized in that a first interlayer connection via, among the interlayer connection vias connecting the layers of the first coil, which is arranged on the outer periphery of the first coil, and a second interlayer connection via, among the interlayer connection vias connecting the layers of the second coil, which is arranged on the outer periphery of the second coil, are arranged on different sides of the center plane. 2. The current sensor according to claim 1, wherein the multilayer printed circuit board is configured with four or more layers. The current sensor described in claim 1 or 2, characterized in that the first coil and the second coil are connected in series so as to reinforce the induced voltages generated by the magnetic field generated by the current flowing through the current bar. A watthour meter that calculates the amount of power flowing through the current bar based on a current signal detected by a current sensor and a voltage signal detected by a voltage sensor described in any one of claims 1 to 3.