JPH10229314A - Terminal noise filter for electric device using inverter power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate effectively common mode noise in the terminal noise filter that eliminates the terminal noise which leaks from an electric device. SOLUTION: A filter circuit, formed by connecting resonance capacitors 3, 4 in parallel with a common mode filter coil 1 and a filter circuit formed by connecting resonance capacitors 5, 6 in parallel with a common mode filter coil 2, are connected in series. Then the resonance frequency of the filter with the inductance L of the common mode filter coils of each filter and the capacitance of the resonance capacitors C is expressed as f=1/2π(LC)<1/2> . The circuit frequency (f) of each filter circuit is selected different from the resonance frequency (f), and the resonance frequency (f) is selected in a range from 50kHz to 500kHz or a multiple of 1 to 5 of an inverter power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal noise filter for removing terminal noise leaking from equipment using an inverter power supply.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional terminal noise filter.
Generally, types of terminal noise are classified into a normal mode and a common mode, and the former uses line-to-line cross capacitors 7 and 8 as means for removing each noise.
The latter uses the common mode filter coil 1 and the ground capacitors 9 and 10.

[0003]

However, in a conventional terminal noise filter of a device using an inverter power supply, especially in a device in which a terminal noise having a strong common mode is generated, the common mode filter coil 1 is enlarged as a means for removing it. Means were taken to do so. In addition, a considerably large one is required for removal. Increasing this increases the size and weight of the terminal noise filter, thus increasing the cost.

There is also a method of increasing the capacity of the earth capacitors 9 and 10. However, when the equipment is not grounded, a current flows to the human body through the earth capacitors 9 and 10 and when a person touches the equipment. There was a problem of feeling abnormal.

[0005] In addition, electromagnetic waves radiated from electronic and electrical devices have become a problem, and are being studied by the International Special Committee on Radio Interference (CISPR) in order to regulate the amount. And
50KH which is difficult to remove with a common mode filter coil or earth capacitor to satisfy this regulation value
Reducing noise at frequencies from 500 kHz to z has been a problem.

[0006]

In order to solve the above-mentioned problems, the present invention comprises a filter circuit for connecting a resonance capacitor in parallel with a common mode filter coil, and further connects the filter circuits in series in multiple stages. Then, the correlation between L of the common mode filter coil of each filter circuit and capacitance C of the resonance capacitor is calculated.

[0007]

(Equation 2)

The frequency f of each filter circuit is set to a different value, and the value of the frequency f is set to 5
The frequency was set between 0 kHz and 500 kHz or 1 to 5 times the operating frequency of the inverter power supply.

According to the above-mentioned invention, the present invention is effective for the frequency band from 50 KHz to 500 KHz which is difficult to remove with the common mode filter coil and the earth capacitor or the fundamental wave of the operating frequency of the inverter power supply to the fifth high frequency. Further, the present invention can be realized without increasing the size of the common mode filter coil. Further, it is not necessary to increase the capacity of the earth capacitor.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, a common mode generated between a line and a ground is not affected by magnetic fluxes induced by a pair of coils with respect to a load current. A circuit comprising a resonance capacitor connected in parallel to each coil of the common mode filter coil acting as a reactance load against noise is provided, and the filter circuits are connected in series in multiple stages. Then, the correlation between the inductance L of the common mode filter coil constituting each filter circuit and the resonance capacitor C is calculated.

[0011]

(Equation 3)

And the frequency f of each filter circuit
Are set to different values, and each frequency f is set to 50K to 50K.
It was set to 0 KHz or 1 to 5 times the operating frequency of the inverter power supply.

[0013] By resonating the parallel circuit of the common mode filter coil and the resonance capacitor at the frequency to be removed, the effect of increasing the impedance and suppressing noise can be obtained.

Therefore, it works effectively from 50 KHz to 500 KHz, which is a frequency band which is difficult to remove with a common mode filter coil or an earth capacitor, or from the fundamental wave of the inverter operating frequency to the fifth high frequency.

Further, the common noise can be effectively removed without increasing the size of the common mode filter coil and without increasing the capacity of the earth capacitor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a terminal noise filter according to an embodiment of the present invention. AC1, AC2 input terminals 11, 12
AC power is input from the
The power that has passed through the terminal noise filters from 3 and 14 is supplied to the power supply load of the device.

Reference numerals 1 and 2 denote common mode filter coils, and FIG. 2 shows their appearance. The coil winding of each line is wound on the same annular core, and its function is that for the overcurrent, the magnetic fluxes induced by the paired coils cancel each other out and affect as a reactive load. However, it acts as an inductive reactance with respect to the common mode noise generated between the line and the ground, and prevents the noise from leaking outside.

Reference numerals 3 and 4 denote resonance capacitors, which are connected in parallel to both ends of the windings of the respective lines of the common mode filter coils 1 and 2. Common mode filter coil 1
, Resonance capacitors 3 and 4 are connected in parallel, and the common mode filter coil 2 is connected with resonance capacitors 5 and 6 in parallel.

The inductances L ₁ and L _{2 of} the common mode filter coils 1 and ₂ and the resonance capacitor 3
Capacity of 4, 5 and 6 C _34, and C _56. However, the case where the resonance capacitors 3 and 4 and 5 and 6 are set to the same capacity in the embodiment is shown. Each combined impedance Z _1, Z ₂ of L ₁ and C ₃₄ and L ₂ and C ₅₆ at this time becomes a parallel circuit of each of L ₁ and C _{3 4,} L ₂ and C _56,

[0020]

(Equation 4)

[0021]

(Equation 5)

## EQU1 ## At this time, 1- (2πf ₁ ) ² C ₃₄ L
₁ = 0, 1- (2πf ₂ ) ² C ₅₆ L ₂ = 0, that is,

[0023]

(Equation 6)

When the [0024], impedance Z1, Z2 becomes infinite, is very large noise blocking the effect of for each of the frequency f _1, f _2. Therefore, if L ₁ , L ₂ , C ₃₄ , and C ₅₆ are determined for the frequency to be blocked, noise can be effectively removed without requiring a large common mode filter coil. Further, by setting f ₁ and f ₂ to different frequencies, the frequency characteristic of the combined impedance of Z ₁ and Z ₂ is widened, and an effect of removing noise over a wide band can be obtained.

FIG. 3 is a circuit diagram of a microwave oven having an inverter power supply using the terminal noise filter of the present invention. From the commercial power supply via the terminal noise filter of the present invention,
Power is supplied to the inverter power supply 15. The inverter power supply 15 supplies a high voltage to the magnetron 23 that generates microwaves. The configuration of the inverter power supply 15 is rectified by the diode bridge 16 to perform DC conversion, and smoothed by the choke 17 and the smoothing capacitor 18. Oscillation occurs due to resonance between the capacitor 19 and the transformer 20, and the oscillation state is controlled by switching of the power transistor 21 based on a signal from the control circuit 22. Generally, the operating frequency of such an inverter power supply is about 20 KHz to 100 KHz. In addition, devices using an inverter power supply are used as a power supply for compressors such as air conditioners and refrigerators in addition to microwave ovens. It is also used in electromagnetic cookers and rice cookers using electromagnetic induction heating. Such devices also have the same noise problem.

The operating frequency of the inverter power supply 15 is 2
Since it is 0 KHz to 100 KHz, it is smoothed by the choke 17 and the smoothing capacitor 18, but the pulsating current of the operating frequency is superimposed on the input current. The waveform is shown in FIG. In particular, equipment using an inverter power supply tends to generate terminal noise.

FIG. 5 shows the frequency characteristics of the impedance of the terminal noise filter according to the embodiment of the present invention. The horizontal axis shows the frequency on a logarithmic scale, and the vertical axis shows the impedance. Z ₁ is maximum at f ₁ and Z ₂ is maximum at f ₂ . Then, by the f ₁ and f ₂ to different values, the combined impedance Z ₁₂ of Z ₁ and Z ₂ are a high value over a wide frequency range as shown in FIG. As a result, the effect of expanding the range of the frequency to be removed is obtained.

FIG. 6 is a spectrum diagram of the terminal noise. The horizontal axis is a logarithmic scale of the frequency, and the vertical axis is the noise voltage which is the terminal noise. 1 μV is 0 dBμV, and the value of v = 20 logV (μV) is shown. I have. The values indicated by the dotted lines in the figure are values that are considered as noise regulation values in CISPR. Therefore,
It needs to be smaller. FIG. 5 shows the spectra of the terminal noise filter of the present invention and the conventional terminal noise filter. (A) shows the present invention and (b) shows the conventional one. (A) is a characteristic when the set frequency f ₁ 60 KHz, the f ₂ to 200 KHz. (A) is smaller at 500 KHz or less than (b), but (a) is larger at 500 KHz or more. However, since (a) has an effect on a frequency band having a higher value than the noise regulation value, the noise regulation value as a whole is satisfied.

The noise regulation value is 150 KHz as shown in FIG.
Since or more, should be determined differences, the optimum value in consideration of the frequency that generates the operating frequency and the noise of the inverter power source for determining the f ₁ and f _2. 3 from the noise threshold of 150 KHz
At 00 KHz, the third to fifth harmonic components of the operating frequency of the inverter power supply are generated as terminal noise. The operating frequency of the inverter power supply is from 20KHz to 100KHz,
Since 3 to 5 times this becomes harmonic noise, 20 KHz
3 to 5 times of 60KHz to 100KHz and 100KH
It becomes 300 KHz to 500 KHz at three times z. Therefore, it is effective to slightly increase the value of f from 50 KHz to 500 KHZ.

Such a common mode noise also occurs in a device that does not use an inverter power supply. For example, it is a device using a motor or a device having a switch operation of a heater or a solenoid. It is effective to use the terminal noise filter for these devices.

[0031]

As described above, according to the terminal noise filter of the present invention, there is an effect that the terminal noise can be reduced in a wide frequency band without increasing the size of the common mode filter coil. There is also an effect of suppressing an increase in cost.

In addition, there is no need to increase the capacity of the earth capacitor, and there is an effect that when a device is not grounded, no abnormality is felt even if a person touches the device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a terminal noise filter of an electric device using an inverter power supply according to an embodiment of the present invention.

FIG. 2 is an external view of a common mode filter coil.

FIG. 3 is a circuit diagram of a microwave oven having an inverter power supply using a terminal noise filter of an electric device using the inverter power supply according to one embodiment of the present invention.

FIG. 4 is an input current waveform diagram of the inverter power supply of the microwave oven.

FIG. 5 is a graph showing impedance characteristics with respect to frequency of a terminal filter of an electric device using the inverter power supply.

FIG. 6 is a noise spectrum diagram for comparing a terminal noise filter of an electric device using the inverter power supply with a conventional terminal noise filter.

FIG. 7 is a circuit diagram of a terminal noise filter of an electric device using a conventional inverter power supply.

[Explanation of symbols]

 1,2 Common mode filter coil 3,4,5,6 Resonant capacitor 15 Inverter power supply

Claims (4)

[Claims] An inverter power supply for converting the frequency of electric power from a commercial power supply to a load, and a magnetic flux induced by a pair of coils with respect to a load current cancels each other and has an effect as a reactance load. Not line
A common mode filter coil acting as a reactance load for common mode noise generated between grounds, and a filter circuit including a resonance capacitor connected in parallel to each coil of the common mode filter coil,
The filter circuits are connected in multiple stages in series, and L of a common mode filter coil constituting each filter circuit.
And the capacitance C of the resonance capacitor as follows: And a terminal noise filter for electrical equipment using an inverter power supply, wherein f of each of the filter circuits is set to a different value. 2. The value of f is set to 1 of the operating frequency of the inverter power supply.
The terminal noise filter of an electric device using the inverter power supply according to claim 1, wherein the terminal noise filter is configured to be five times as large as. 3. The terminal of an electric apparatus using an inverter power supply according to claim 1, wherein the value of f is mixed with a value of 50 KHz to 500 KHz and a value of 1 to 5 times the operating frequency of the inverter power supply. Noise filter. 4. The terminal noise filter of an electric device using an inverter power supply according to claim 1, wherein the value of f is set to a value from 50 KHz to 500 KHz.