JP2000235051A - Detector for detecting direct current component contained in alternating current - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly precisely detect a direct current component contained in an alternating current, without using a highly precise Hall element type current transformer or a high-cut filter. SOLUTION: A direct current component detector 20 is composed of an electromagnetic type current transformer 21 with current transformation ratio of (n) and a Hall element type current transformer 22, and it is arranged in an alternating current main circuit 23. Total current of an alternating current IAC and a direct current component IDC are flowed in the main circuit 23, and a secondary circuit 21S of the transformer 21 outputs a current of IAC/n. An auxiliary coil 22A with a wound number of (n) is provided in a ring-like iron core 22C of the Hall element transformer 22 to be connected to the secondary circuit 21S, and a magnetic flux of the alternating current IAC out of magnetic fluxes resulting from IAC+IDC generated in the iron core 22C is offset each other with a magnetic flux generated in the auxiliary coil 22A. A remaining magnetic flux of the direct current component IDC is detected by a Hall element 22H provided in a gap of the iron core 22C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting a direct current component contained in an alternating current, which can detect a direct current component contained in an alternating current flowing in an alternating current circuit with high accuracy.

[0002]

2. Description of the Related Art Generally, electric power used by households is received from a commercial electric power system operated by an electric power company, except for a special environment such as a remote island. However, if natural energy such as sunlight, solar heat, wind power, and wave power is converted to electric power and used, electric power can be obtained without deteriorating the natural environment. Power generation devices using such natural energy have been installed in various places. Also,
Fuel cells are increasingly used because they are low-pollution electrical energy sources. Most of these are power sources that generate DC power, and among these power sources, a photovoltaic power generation system (hereinafter abbreviated as a solar cell) that generates power using solar light energy is the most widely used. Therefore, the details of the present invention will be described below using a solar cell as an example.

Power demand at home is higher at night than at daytime, but power generation by solar cells is only at daytime, and the amount of power generated at night is zero. The amount of power generation is greatly reduced compared to when the weather is fine. In this way, the amount of power supplied by solar cells fluctuates greatly depending on external conditions, and it is impossible to satisfy 100% of household power demand. Therefore, it is common to provide a facility that can receive power from the commercial power system when the power generated by the solar cell is insufficient, but the surplus power generated by the solar cell is stored in, for example, a secondary storage battery. In addition, there is a method of using the energy stored in the secondary storage battery as needed. However, even in the latter case, the power may still be insufficient just by providing the secondary storage battery. Therefore, it is usual to provide a facility capable of receiving the insufficient power from the commercial power system. When a solar cell is installed in this manner, a facility capable of receiving power from a commercial power system regardless of the presence or absence of a secondary battery is provided.

[0004] FIG. 2 is a single-line circuit diagram showing a general connection state in a case where a photovoltaic power generator is connected to a commercial power system by a single line. In FIG. 2, a photovoltaic power generation device 5 includes a solar cell 2 installed on a roof of a house or the like for converting the light energy of the sun into DC power, and an inverter 3 for converting the DC power into AC power. The DC power generated by the solar cell 2 is converted into AC power by the inverter 3 and supplied to the load 6. The interconnecting switch 8 is a switch for closing the load when the power generated by the solar cell 2 alone cannot meet the demand of the load 6 and supplying power from the commercial power system 7 to the load 6. is there. Therefore, the interconnection switch 8
Passes through the commercial power system 7 in the direction of the photovoltaic power generator 5 (in the direction of the arrow). In order to measure this power, an electromagnetic current transformer 11 is inserted between the interconnection switch 8 and the load 6, and the current flowing therethrough is measured.

[0005] In the daytime on a sunny day or the like, even if the power generated by the solar cell 2 can cover the demand of the load 6, a surplus may still occur, but conventionally, the surplus power is not used effectively. Although the waste power was wasted, recently, the surplus power has been able to be effectively used by being sent to the commercial power system 7. That is, the electric power passing through the interconnection switch 8 is changed in the conventional one direction (the direction from the commercial power system 7 to the photovoltaic power generator 5, that is, the arrow direction), but also in the opposite direction. You can now run. By flowing power in the opposite direction, the amount of power generated by the commercial power system 7 can be reduced, so that a greater energy saving effect can be obtained.

However, the photovoltaic power generator 5 is connected to the commercial power system 7.
When a failure (for example, a power outage or the like) occurs in the commercial power system 7 due to the failure of the photovoltaic power generator 5 when interconnecting to a general customer, general consumers are greatly inconvenienced. Become. Therefore, various restrictions are imposed on the photovoltaic power generation device 5 so that such a problem does not occur. One of the restrictions is suppression of outflow of a DC component current to the commercial power system 7. That is, the "distributed power supply system interconnection technical guideline" stipulates that the DC component current outflow protection is performed at 1% of the rated output current.

The solar cell 2 outputs DC power, while the general load 6 operates on AC power. In order to output the AC power from the photovoltaic power generator 5, an inverter 3 for converting the DC power into the AC power is provided. The AC power output from the inverter 3 has a small DC component. For example, one of the causes of the presence of a direct current component is that the operating time and operating characteristics of the positive-side semiconductor switch element constituting the inverter 3 are slightly different from those of the negative-side semiconductor switch element. Since the output AC power of the inverter 3 may include a DC component exceeding the specified level due to the above-mentioned cause or another matter, it is necessary to protect the outflow of the DC component current based on the above technical guidelines. Must first detect the direct current component current. However, the electromagnetic current transformer 11 used in the circuit of FIG.
Can only detect alternating current.

FIG. 3 is a single-line circuit diagram showing a conventional example for detecting a DC component current included in an alternating current output from a photovoltaic power generation system connected to a commercial power system by a single line.
The conventional circuit shown in FIG. 1 is provided with a Hall element type current transformer 12 and a high cut filter 13 in place of the electromagnetic current transformer 11 used in the above-described general circuit of FIG. However, since the other parts are the same as those of the general circuit described above with reference to FIG. 2, the description of the same parts will be omitted.

The Hall element has a constant current I in its specific direction.
_When a magnetic flux having a magnetic flux density B is applied in a direction perpendicular to this current, a Hall electromotive force V _H is generated in the direction perpendicular to both the constant current I _C and the magnetic flux B. The magnitude of the electromotive force V _H is proportional to the product of the constant current I _C and the magnetic flux B. Thus, it is possible to know the magnitude of the magnetic flux B by measuring the Hall electromotive force V _H. The Hall element type current transformer 12 is configured by providing a plurality of gaps in a ring-shaped iron core, and separately inserting the above-described Hall elements in each of the gaps. A conductor through which the main circuit current flows passes through the center of the ring-shaped iron core. Since the magnetic flux B changes according to the magnitude of the main circuit current, the Hall electromotive force V _H
Is measured, the magnitude of the main circuit current can be known. This Hall element type current transformer 12 has
It can detect whether the main circuit current is AC or DC. Therefore, the high cut filter 13 is connected to the Hall element type current transformer 12.
Is connected to remove the AC current of the commercial frequency from the detection current, only the DC component current included in the AC current output by the photovoltaic power generator 5 can be detected.

As described above, when the photovoltaic power generator 5 is interconnected with the commercial power system 7, the electric power passing through the interconnection switch 8 is bidirectional as indicated by the arrow. At what point in time the system switch 8 is opened and closed is irrelevant to the present invention, and a description thereof will be omitted.

[0011]

In the conventional circuit described above with reference to FIG. 3, the DC current is detected by combining the Hall element type current transformer 12 and the high cut filter 13, but it is constituted by electronic components. High cut filter 13
However, it is difficult to detect the DC component current with high accuracy because the characteristics change due to the temperature drift of the components. The output of the Hall element type current transformer 12 generally has an offset error of about 1% of the rated output. Even if the technical guidelines stipulate that DC component current outflow protection is performed at 1% of the rated output current, it is difficult to distinguish the actual DC component current from the offset error if there is an offset error of 1%. is there. In addition to this, an error due to the temperature drift of the high cut filter 13 is further added. Therefore,
There is a disadvantage that the Hall element type current transformer 12 which is more accurate and expensive than usual is adopted, and the high cut filter 13 must be used with high accuracy and expensive.

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to detect a DC component current contained in an AC current with high accuracy without using a high-precision Hall element type current transformer or a high cut filter. .

[0013]

In order to achieve the above object, a DC component current detecting device included in an AC current according to the present invention comprises an AC main circuit comprising an electromagnetic current transformer and a Hall element type current transformer. Is installed, and the alternating current component of the main circuit current detected by the Hall element type current transformer is offset by the secondary current detected by the electromagnetic current transformer.

An auxiliary coil having a predetermined number of turns is provided on the ring-shaped iron core of the Hall element type current transformer, and a secondary current of the electromagnetic current transformer is caused to flow through the auxiliary coil, whereby the Hall element type current transformer is provided. The magnetic flux due to the alternating current component of the magnetic flux due to the main circuit current generated in the ring-shaped core of the vessel is offset by the magnetic flux of the auxiliary coil.

[0015]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, a DC component current detecting device 2
Numeral 0 designates an electromagnetic current transformer 21 and a Hall element type current transformer 22, both of which are installed in an AC main circuit 23 through which an AC current including a DC component flows.
, A current equal to the sum of the _{AC component} current I _AC and the DC component current I _DC flows. The AC main circuit 23 corresponds to a line connecting the interconnection switch 8 and the load 6 in the above-described conventional circuit of FIG.

The electromagnetic current transformer 21 detects only the AC current I _AC in the main circuit current. Therefore, assuming that the current transformer ratio of the electromagnetic current transformer 21 is n, the secondary circuit 21S of the current transformer 21 has I _AC /
A current of n flows. On the other hand, a magnetic flux due to the main circuit current I _AC + I _DC is generated in the ring-shaped core 22C of the Hall element type current transformer 22. Therefore, this ring-shaped iron core 22C
Is provided with an auxiliary coil 22A having n turns and connected to the secondary circuit 21S of the electromagnetic current transformer 21 described above.
The auxiliary coil 22A generates a magnetic flux due to the _AC current I _AC, and the polarity of the magnetic flux generated by the auxiliary coil 22A is opposite to the magnetic flux due to the main circuit current I _AC + I _DC described above. Polarity. As a result, the AC current I _AC
The magnetic flux due to is canceled. Therefore, the Hall electromotive force k · V _H obtained from the Hall element 22H (where k is a constant)
Is measured, the main circuit current I _AC flowing through the AC main circuit 23 is obtained.
The value of the _{DC component} current I _DC included in + I _DC can be detected.

As described above, in the ring-shaped iron core 22C, the magnetic flux due to the AC current I _AC is canceled out to be zero, and only the magnetic flux due to the _{DC component} current I _DC remains. However, the DC component current I
_DC is generally much smaller than the _AC current I _AC , for example, if it is about 5% of the _AC current I _AC , the rating of the Hall element type current transformer 22 for detecting this DC component current I _DC The current may be 5% of the rated current of the electromagnetic current transformer 21 for detecting the _AC current I _AC . Even if the offset error of the Hall element type current transformer 22 is 1%, this is 0.05% with respect to the rated value of the alternating current. Therefore, even if a Hall element type current transformer 22 having a normal offset error is used to detect 1% of the rated output current for the DC component current outflow protection required by the above technical guideline, The offset error has a small value that can be ignored.

[0018]

According to the present invention, when a DC power supply such as a solar cell is connected to a commercial power system, a device for detecting a DC component current included in an AC current by combining a Hall element type current transformer and a high cut filter. Therefore, it is difficult to provide DC current leakage protection at 1% of the rated output current required by the technical guidelines due to errors due to temperature drift of the high-cut filter and offset errors of the Hall element type current transformer. Was. Therefore, a non-standard and expensive high-cut filter to reduce the temperature drift and a non-standard and expensive Hall element type current transformer to reduce the offset error as much as possible will be used, resulting in a longer delivery time. And various other problems.

According to the present invention, an auxiliary coil having a predetermined number of turns is provided on a ring-shaped core of a Hall element type current transformer capable of detecting both AC and DC currents, and a secondary circuit of the electromagnetic current transformer is connected to the auxiliary coil. The magnetic flux generated in step (1) cancels the magnetic flux generated by the alternating current in the ring-shaped iron core. As a result, it is possible to detect the Hall electromotive force corresponding to the DC component current from the Hall element inserted into the ring-shaped iron core. Therefore, an expensive high-cut filter which causes an error due to temperature drift is not required. Further, since the Hall element type current transformer only needs to be able to detect a DC component current, its rated current can be selected to be small. Therefore, even if the Hall element type current transformer has the same offset error as the conventional one, the ratio of the offset error to the rated current can be much smaller than the technical guideline of 1%. There is no need to use it. As a result, the effect of suppressing the size of the device and reducing the price can be obtained despite the fact that the DC component current is detected with high accuracy.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a single-line circuit diagram showing a general connection state when a solar power generation device is connected to a commercial power system with a single line.

FIG. 3 is a single-line circuit diagram showing a conventional example of detecting a DC component current included in an alternating current output from a photovoltaic power generation system connected to a commercial power system with a single line.

[Explanation of symbols]

 2 Solar cell 3 Inverter 5 Photovoltaic power generator 6 Load 7 Commercial power system 8 Interconnection switch 12,22 Hall element type current transformer 11,21 Electromagnetic type current transformer 13 High cut filter 20 DC current detection device 21S Electromagnetic Circuit of secondary current transformer 22A Auxiliary coil of Hall element type current transformer 22C Ring-shaped core of Hall element type current transformer 22H Hall element 23 AC main circuit

Claims (2)

[Claims] An electromagnetic current transformer and a Hall element type current transformer are installed in an AC main circuit, and an alternating current component of a main circuit current detected by the Hall element type current transformer is converted to the electromagnetic type current. A DC component current detecting device included in an AC current, wherein the DC component current is offset by a secondary current detected by a current transformer. 2. An annular current transformer having an electromagnetic current transformer and a Hall element type current transformer installed in an AC main circuit, and a ring-shaped core of the Hall element type current transformer according to a main circuit current flowing through the Hall element type current transformer. Auxiliary coils of the polarity and the number of turns that cancel out the magnetic flux due to the alternating current component of the magnetic flux generated by the secondary current of the electromagnetic current transformer are included in the alternating current characterized in that the ring-shaped iron core is provided. DC component current detector.