JPH10262364A - Electric equipment using inverter power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress terminal noise by constituting a choke circuit having a choke coil for suppressing pulsating current or noise by on-off operation of a switching element and connected to a resonance capacitor for choke in parallel with the coil. SOLUTION: Noise or pulsating current is generated at input current of an inverter power source due to on-off operation of a switching element 6. To reduce this terminal noise, a choke circuit having a choke coil 9 connected in parallel with a resonance capacitor 17 for choke is connected to a common mode filter coil 12 of a terminal noise filter 16 and resonance capacitors 19, 20 for the common mode filter in parallel with windings of the coil 12. And, inductances and capacitances are suitably set to reduce the noise or pulsating current.

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 suppressing terminal noise leaking from equipment using an inverter power supply.

[0002]

2. Description of the Related Art FIG. 8 is a circuit diagram of a microwave oven as an embodiment of a conventional electric device using an inverter power supply.
FIG. 8 shows a conventional terminal noise filter 1 and a conventional inverter power supply 2. With respect to the conventional inverter power supply 2, the commercial power supply is rectified by the diode bridge 3 to DC,
The power is oscillated by an ON / OFF operation of the switching element 6 in an oscillating circuit composed of the oscillating capacitor 4 and the transformer 5 to control the power supplied to the magnetron 7 as a load.
A smoothing capacitor 8 and a choke coil 9 are provided to suppress the pulsating flow and noise of the input current generated by the F operation.

[0003] The configuration of a conventional terminal noise filter 1 will be described. Generally, types of terminal noise are classified into a normal mode and a common mode. As means for suppressing the respective noises, the former uses cross capacitors 10 and 11 between lines, and the latter uses a common mode filter coil 12 or a ground. The capacitors 13 and 14 were used. Reference numeral 15 denotes a control circuit for controlling the operation of the switching element 6.

[0004]

However, in the conventional inverter power supply 2, a choke coil 9 and a smoothing capacitor 8 are provided in order to suppress the pulsating flow and noise of the input current.
Measures were taken to increase the When the size of the smoothing capacitor 8 is increased, there is a problem that a charging current instantaneously flows through the smoothing capacitor 8 when the power is turned on, and a large rush current is generated. In order to increase the size of the choke coil 9, it is necessary to increase the size of the choke coil by three to five times.
There is a problem that the weight is large and the cost is increased.

Further, in the conventional terminal noise filter 1, especially in a device using an inverter power supply in which terminal noise having a strong common mode is generated, means for increasing the size of the common mode filter coil is used as means for suppressing the noise. I was If this is increased, a considerably large one is required, and a dimension is required to be three to five times or more, and there is a problem that the weight is large and the cost is increased. There is also a means for increasing the capacity of the ground capacitors 13 and 14. However, if the device is not grounded, when a person touches the device, current flows through the human body through the earth capacitors 13 and 14 and the user feels abnormal. Therefore, there is a problem that there is a limit in increasing the size of the earth capacitor.

[0006]

The present invention has been made to solve the above problems. Regarding the inverter power supply, a choke coil for suppressing pulsation and noise due to the ON-OFF operation of the switching element and a choke resonance capacitor 5 connected in parallel with the choke coil are configured. And the inductance L of the choke coil
_C and the capacitance C _C of the choke resonance capacitor

[0007]

(Equation 2)

The value of f _C is set to a frequency effective for suppressing terminal noise. As for the terminal noise filter, a common mode filter resonance capacitor is connected in parallel with the common mode filter coil. Then the correlation between inductance L _f and the capacitance C _f of the resonance capacitor common mode filter of the common mode filter coil

[0009]

(Equation 3)

Then, the value of _ff is set to a frequency effective for suppressing terminal noise. Further, in order to effectively suppress a wide frequency range, it is possible by setting to a different frequency values for f _C and f _f.

Further, it is effective to set the f _C and f _f especially from the first as a harmonic of the operating frequency of the inverter power supply to the fifth harmonic.

Further, f _C and _ff are set to 50KHz to 500K.
Setting to Hz is also effective. This is because the regulation of terminal noise is being studied internationally by the International Commission on Radio Interference (CISPR), and the regulation value is being considered from 150 KHz. From 150 KHz, the third to fifth harmonics of the operating frequency of the inverter power supply correspond to this, and it is also a difficult frequency band to suppress these frequencies. Therefore, the operating frequency of the inverter power supply is generally 20
KHz to 100 KHz, and three to five times these are harmonic noises.
Hz, 5 times of 100 kHz, becomes 500 kHz. Therefore it is effective to set the f _C and f _f to 500KHz from 50 KHz.

[0013] Also, _ff is from 50 KHz to 500 KHz.
Set, 500K or set f _c to 5 times the first operating frequency of the inverter power supply, the fc reversed from 50KHz
And Hz, it may be set f _f 5 times from 1 of the operating frequency of the inverter power supply.

With the above arrangement, the size of the smoothing capacitor can be increased, and as a result, inrush current can be prevented. Further, it is not necessary to increase the dimensions of the choke coil and the common mode filter coil, and the cost can be prevented from increasing. Further, it is not necessary to increase the capacity of the earth capacitor.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a diode bridge for rectifying a commercial power supply, a switching element for controlling power supplied to a load, a choke coil for suppressing noise generated by the operation of the switching element, and a choke coil in parallel with the choke coil. Inverter power supply consisting of a choke resonance capacitor connected to the inverter and a common current generated between the earth and the line without influencing the load current due to the magnetic fluxes induced by the paired coils canceling each other and reacting as a load. A common mode filter coil acting as a reactance load against mode noise, and a common mode filter resonance capacitor connected in parallel to each coil of the common mode filter coil, wherein the choke coil inductance L _{C is changed} to a choke resonance capacitor. Capacity C _C and common Each correlation between inductance L _f and the capacitance C _f of the resonance capacitor common mode filter of the mode filter coil,

[0016]

(Equation 4)

And [0017], a configuration of setting the f _C and f _f a valid value to suppress terminal noise. This is L _C and C _C
By resonating at frequencies where L _f and C _f are desired to be suppressed, the impedance is increased and the effect of suppressing noise can be obtained.

Further, by setting different values f _C and f _f, expanding the range of frequencies can be suppressed, the effect of suppressing noise over a wide band can be obtained.

[0019] By further setting the f _C and f _f the fifth harmonic of the frequency from the first high as harmonic components of the inverter power supply can be effectively suppressed noise generated from the inverter power supply.

Further, f _C and _ff are changed from 50 KHz to 500 KHz.
Setting to Hz is also effective. The regulation value of the terminal noise is considered internationally and is regulated from 150 KHz or more. It is difficult to suppress noise at this frequency, especially the third to fifth harmonics of the inverter power supply, and the frequency is about 50 kHz to 500 kHz.
Becomes

Furthermore, it can be suppressed also effectively noise by setting a combination of frequencies of 500KHz respectively f _c and f _f from the frequency and 50KHz five times the first inverter power source operating frequency.

Further, it is not necessary to increase the size of the smoothing capacitor, choke coil, common mode filter coil, earth capacitor, and the like.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a microwave oven as an electric device using the inverter power supply of the present invention. Also,
2 (a) and 2 (b) show a terminal noise filter 16 and a choke circuit composed of the choke coil 9 and the choke resonance capacitor 17, respectively.

In FIG. 1, power input from a commercial power supply passes through a terminal noise filter 16 and is supplied to an inverter power supply 1.
8 is input. The input power is rectified by the diode bridge 3 and exchanged with direct current. The DC-exchanged power is supplied to an oscillation capacitor 4 and a transformer 5 that constitute an oscillation circuit, and the power supply amount is controlled by a switching element 6. The switching element 6 operates according to a signal from the control circuit 15. The control circuit 15 turns ON / OFF the switching element 6 in accordance with the amount of power supplied to the load.
To control the operating frequency and duty. The power boosted by the transformer 5 is supplied to the magnetron 7 as a load. Generally, the operating frequency of such an inverter power supply is about 20 kHz to 100 kHz. The ON-OFF operation of the switching element 6 causes noise and pulsation to occur in the input current of the inverter power supply. The waveform is shown in FIG. A radio wave in which a pulsating flow is superimposed on the frequency of the commercial power supply of 50/60 Hz flows, and a large terminal noise is generated.

According to the present invention, in order to reduce the terminal noise, the choke circuit including the choke coil 9 and the choke resonance capacitor 17 connected in parallel with the choke coil 9, the common mode filter coil 12 of the terminal noise filter 16, The resonance capacitors 19 and 20 for the common mode filter are connected in parallel to the respective windings of the common mode filter coil, and noise and pulsating current are reduced as shown in FIG. be able to.

First, a choke circuit including the choke coil 9 and the choke resonance capacitor 17 will be described. FIG. 2B shows the circuit configuration. FIG. 4 shows the appearance of the choke coil 9. There is a method of increasing the size and the number of turns of a coil in which a coil is wound around a core to increase the ability to suppress pulsating flow and noise. However, the method is large in size, large in weight and high in cost. Therefore, by connecting the choke resonance capacitor 17 in parallel with the choke coil 9, a device having an appropriate suppression capability can be realized. The combined impedance Z _C of the inductance L _C of the choke coil 9 and the capacitance C _C of the choke resonance capacitor 17 becomes a parallel circuit of L _C and C _C ,

[0027]

(Equation 5)

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

[0029]

(Equation 6)

Then, the impedance Z _C becomes infinite, and the effect of suppressing noise with respect to the frequency f _C is extremely large. Therefore, if the value of f _C is set to a frequency effective for suppressing terminal noise, a large choke coil 9 is not required.

Next, another terminal noise filter 16 will be described. FIG. 2A shows the circuit configuration. A _C 1, the commercial power supply from the input side of the A _C 2 is input, it is supplied to the inverter power supply 18 as a load from the output side of the A _C 3, A _C 4. A common mode filter coil 12 is shown in FIG. The coil winding of each line is wound around a single annular core, and its function is that although the magnetic fluxes induced by the paired coils cancel each other against the load current, they do not affect the reactance load. In addition, it acts as an inductive reactance with respect to common mode noise generated between the line and the ground, preventing leakage of the noise to the outside. 19 and 20 are common mode filter resonance capacitors, which are connected in parallel to the respective coils of the common mode filter coil 12. Then, the combined impedance Z _f of the inductance L _f and the capacitance C _f of the common mode filter for resonant capacitor 19 and 20 of the common mode filter coil 12 becomes a parallel circuit of L _f and C _f,

[0032]

(Equation 7)

## EQU1 ## At this time ^{_{1- (2πf f) 2 C f}} L f =
0, ie

[0034]

(Equation 8)

When the [0035], impedance Z _f becomes infinite, it is very large effect of noise of the blocking for the frequency _f f. Therefore, the frequency f effective for suppressing noise
_If L _f and C _f are set for _f , a large common mode filter coil 12 is not required.

FIG. 6 shows the frequency characteristics of the impedance Z _C of the choke circuit and the impedance Z _f of the terminal noise filter of the electric equipment using the inverter power supply 11 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 _C is maximum at f _C and Z _f is maximum at _ff . Then, by the different values f _C and f _f, the combined impedance Z _Cf of Z _f and Z _C is a high value over a wide frequency range as shown in FIG.
As a result, an effect is obtained in which the range of frequencies for suppressing noise is widened.

FIG. 7 is a spectrum diagram of terminal noise.
The horizontal axis represents frequency on a logarithmic scale, and the vertical axis represents terminal noise voltage. The vertical axis indicates that 1 μV is OdBμV, and V (dBμ
V) = 20 logV (μV). The values indicated by the dotted lines in the figure are values that are being studied as noise regulation values, and are being studied internationally by the International Commission on Radio Interference (CISPR). Therefore, it must be smaller than this. The terminal noise spectra of the present invention and the conventional terminal noise are shown.
(A) shows the present invention, and (b) shows the conventional one.
(A) is a terminal noise when setting f _c 60 KHz, a f _f to 200 KHz. (A) is 5 compared to (b)
It is small below 00 KHz, but it is large above 500 KHz. However, since (a) is more effective for a frequency that is higher than the regulation value, the regulation value is satisfied as a whole.

[0038] For regulating value is more than 150KHz as shown in FIG. 7, when determining f _c and f _f, the inverter power supply 1
1 should be set to an optimum value in consideration of the operating frequency and the frequency at which noise occurs.

In order to suppress a wide frequency range, f
and _c and f _f it is effective to set a different value.

Further, the f _c and f _f as harmonics of the operating frequency of the inverter power supply can be particularly effectively suppressed noise is also generated from the inverter power supply can be set from the first to the fifth harmonic.

[0041] In addition, 500K a f _c and f _f from 50KHz
Setting to Hz is also effective. This is because the regulation of terminal noise is from 150 KHz, and this value corresponds to the third to fifth harmonics of the operating frequency of the inverter power supply 11, and frequency noise near the third to fifth harmonics is also generated.
These frequencies are also difficult to suppress. Therefore, the operating frequency of the inverter power supply 11 is generally from 20 kHz to 100 kHz, and is about 50 kHz at three times 20 kHz and 500 kHz at five times 100 kHz. It is effective to set the f _c and f _f to 500kHz from therefore 50 kHz.

Further, _{ff is set} to 50 kHz to 500 kHz.
Set, 1 f _c of the operating frequency of the inverter power supply 11
You can set to 5 times, 5 Gyakun'i f _c from 50kHz
Setting the f _f set to 00kHz to 5 times the first operating frequency of the inverter power supply 11, effectively noise suppression capability.

Setting the frequency from 50 kHz to 500 kHz is effective not only for harmonics but also for noises of different frequencies generated by the harmonics.

[0044]

As described above, in the electric equipment using the inverter power supply of the present invention, the size of the smoothing capacitor is increased, and as a result, the occurrence of inrush current can be prevented. Also, there is no need to increase the dimensions of the choke coil and the common mode filter coil. Further, there is no need to increase the capacity of the earth capacitor, and no abnormality is felt even if a person touches the device when the device is not grounded.

Further, the effect of strongly suppressing noise can be obtained over a wide frequency range.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a microwave oven as an electric device using an inverter power supply according to one embodiment of the present invention.

FIG. 2A is a circuit diagram of a terminal noise filter of an electric device using the inverter power supply. FIG. 2B is a circuit diagram of a choke circuit of the electric device using the inverter power supply.

FIG. 3 (a) Input current waveform diagram of a conventional microwave oven inverter power supply (b) Input current waveform diagram of a microwave oven inverter power supply using the inverter power supply of the present invention

FIG. 4 is an external view of a choke coil.

FIG. 5 is an external view of a common mode filter coil.

FIG. 6 is a graph showing impedance characteristics with respect to frequency of a terminal noise filter and a choke circuit of an electric device using an inverter power supply according to one embodiment of the present invention.

FIG. 7 is a noise spectrum diagram for comparing the intensity of terminal noise of electric equipment using the inverter power supply.

FIG. 8 is a circuit diagram of a microwave oven as an electric device using a conventional inverter power supply.

[Explanation of symbols]

 2 Inverter power supply 3 Diode bridge 6 Switching element 9 Choke coil 12 Common mode filter coil 17 Choke resonance capacitor 19, 20 Common mode filter resonance capacitor

Claims (7)

[Claims] 1. A diode bridge for rectifying a commercial power supply, a switching element for controlling power supplied to a load, a choke coil for controlling noise generated by the operation of the switching element, and a choke connected in parallel to the choke coil. An inverter power supply having a resonant capacitor;
A common mode filter coil acting as a reactance load against common mode noise generated between the ground and the line without the magnetic fluxes induced by the paired coils canceling each other against the load current and affecting each other as a reactance load, An electric device using an inverter power supply including a common mode filter resonance capacitor connected in parallel to each of the common mode filter coils. 2. The inductance L _{C of the} choke coil.
And the inductance L _{C of the} choke coil and the capacitance C _C of the choke resonance capacitor, and the correlation between the inductance L _f of the common mode filter coil and the capacitance C _{f of the} resonance capacitor for the common mode filter. ] And then, an electric device using an inverter power supply according to claim 1, wherein where the structure is set to a valid value to suppress terminal noise of f _c and f _f. 3. Electrical equipment using an inverter power supply according to claim 1 or 2 wherein where the structure to set the f _c and f _f to different values. The value of 4. f _c or f _f from 50 KHz 500
An electric device using the inverter power supply according to claim 1 or 2 set to KHz. 5. An electric equipment using an inverter power supply according to claim 1 or 2, wherein setting the value of f _c or f _f 5 times from 1 of the operating frequency of the inverter power supply. 6. The electrical device the value of f _f set from 50KHz to 500 KHz, and was used an inverter power values of f _c according to claim 1 or 2, wherein the set of one of the operating frequency of the inverter power supply 5 times . 7. 500K values of f _f set vital f _c 1 of the operating frequency of the inverter power supply to 5 times 50KHz
An electric device using the inverter power supply according to claim 1 or 2 set to Hz.