JP3155912B2 - Electric shock prevention circuit in electrical equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stray capacitance existing between an output line on the output side of a power conversion device provided in a housing of an electric equipment to which an AC power source is input and a housing, and a negative capacitance. The present invention relates to a circuit for reducing a voltage generated in a housing due to a stray capacitance existing between a load input side and the housing and preventing electric shock of a human body even when the housing is not grounded.

[0002]

2. Description of the Related Art FIG. 6 shows an example of an electric device 4 having a power converter 2 and a load 3 in a housing 1. The housing 1 is a container mainly made of a conductor such as an iron plate and having the same electrical potential and for mounting and housing electrical components. The electric device 4 includes, for example, three-phase AC power supplies R1, S1,
The earth leakage breaker 6 is connected to T1 and the input R of the power converter 2 is
2, S2, and T2. The power converter 2 generally rectifies an AC voltage, converts it to a DC voltage, and outputs a desired voltage waveform to the load 3 by a switching element. For example, the power converter 2 of FIG. 6 rectifies the voltages of the inputs R2, S2, and T2 by the diodes 10 to 15 and converts them into a DC voltage. This DC voltage is smoothed by the large-capacity capacitor 16 to become a constant DC voltage. Switching element 20 ~
25 switches at a high frequency by, for example, PWM control (pulse width modulation control) and outputs a waveform such as a low frequency sine wave to the outputs U1, V1, and W1. If the load 3 is, for example, a motor, it does not respond to the high frequency of the PWM control,
It is driven by a low frequency sine wave voltage. The load 3 is attached to the housing 1, and the housing 1 is normally connected to a ground terminal E and grounded (earthed). The conventional electric device 4 is configured as described above.

Next, the cause of the electric shock will be described. The outputs U1, V1, and W1 of the power converter 2 have a stray capacitance with the housing 1 when the wiring distance is long. The input terminals U2, V2, and W2 of the load 3 also have a stray capacitance with the housing 1. For example, in the case of a load 3 such as a motor, 2000 to 50
There is a stray capacitance of 00 pF. Let these stray capacitances be Cu, Cv, and Cw for the outputs U1, V1, and W1, respectively.
The leakage current flowing through each stray capacitance is represented by iu, iv, i
Assuming that w, for example, a leakage current iu flowing to the stray capacitance Cu of the output U1 is determined by a change in voltage between the output U1 and the housing 1. The total current ie of the leakage currents iu, iv, iw flows as the leakage current when the ground terminal E of the housing 1 is grounded. Then, currents having the same current value flow through the inputs R2, S2, and T2 as zero-phase currents. Therefore, voltage changes of the outputs U1, V1, W1 are caused by the leakage currents iu, iv,
iw, which is a zero-phase current that is the sum of the leakage current to the ground and each phase current of the three-phase AC power supply 5. If the housing is not grounded, the housing has a voltage with respect to the ground, and there is a risk of electric shock when a human body comes into contact. In particular, the stray capacitances Cu, Cv, and Cw of the load 3 are large, and the higher the switching frequency of the power converter 2, the higher the voltage, which is dangerous. Also, the leakage current when a human body comes into contact is large.

FIG. 7 shows waveforms at various parts of the conventional electric device 4 shown in FIG. 30 in (a) is R1-S1 of the three-phase AC power supply 5.
It is a voltage waveform between. Similarly, 31 is between S1 and T1, 32
Is the voltage waveform of S1. Since the three-phase AC power supply 5 has S1 grounded, the voltage of S1 at 32 in FIG. 7A is zero. (B) is a voltage waveform after rectifying the three-phase alternating current of the power converter 2. 33 is a plus-side P potential and 34 is a minus-side N potential. 35 indicates an intermediate voltage between P and N. Although the voltage between P and N is constant by the large-capacity capacitor 16, the operating voltage of the power converter 2 with respect to the ground is a low-frequency AC voltage distorted as 35 due to the conducting phase of the diodes 10 to 15. . Switching element 2
Each of 0 to 25 switches the output to the P potential or the N potential at a high frequency by switching. For example, if the switching element 20 is turned on, the output U1
Becomes the potential of P, and when the switching element 21 is turned on, the output U1 becomes the potential of N. Therefore, the potential of the output U1 changes at a high frequency (carrier frequency) of the PWM control.
As described above, the outputs U1, V1, and W1 include the switching elements 20 to in addition to the low-frequency potential change in which P and N change as shown in (b) 33 and 34 of FIG.
The potential changes at a high frequency due to 25 switchings. P and N when the line voltage of the three-phase AC power supply 5 is 200 V
Is about 270V.

FIG. 8 is an enlarged view of a portion 36 in FIG. 7B. (A) is a voltage waveform of the output U1, and is a waveform 40 in which the switching elements 20 and 21 are alternately switched. The waveform 40 has, for example, a carrier frequency of 15
It becomes a substantially rectangular wave of KHz. Since the voltage change is steep in the portion 41 of the voltage waveform 40 at the time of switching, the current waveform of the leakage current iu flowing to the stray capacitance Cu is
Is grounded (b) As shown in FIG.
A large leakage current of 2 A or more flows. 7B is a period during which the potentials of P and N are rising, and the portion 43 of FIG.
Although a positive current flows as a current waveform of the leakage current iu flowing through the circuit, the leakage current is slight because the voltage change is slow. Therefore, most of the leakage current is
25 is generated by switching at a high frequency, and a large leakage current flows even with a small stray capacitance. Therefore, when the housing 1 is not grounded and a human body comes into contact, the voltage of the waveform 40 in FIG. 8A is changed to the stray capacitances Cu, Cv, and C.
In the worst case (b), the current flows through w, and there is a risk of electric shock.

<Documents Related to the Related Art> There are the following documents related to the related art. 1. Ogasawara, Fujita, Akagi: "Modeling and theoretical analysis of high-frequency leakage current generated by voltage-type PWM inverter", IEEJ Transactions on Industry Applications D (Volume of Industrial Applications), Vol. 115-
D, No. 1, P. 77-83, 1995 2. Shimizu, Hu, Kimura, Hirose: "Reduction method of high-frequency leakage current by suppressing AC neutral point potential fluctuation," IEICE Technical Committee.
Technical Committee on Semiconductor Power Conversion SPC-95-31, June 9, 1995 3. Published Utility Model Publication No. 62-88484 "Electric leakage prevention device"

[0007]

Since the conventional electric device 4 is configured as described above, if the housing 1 is not grounded, or if the grounding is incomplete, the ground wire may be disconnected or cut off. In the case where high frequency leakage current is stray capacitance Cu,
There is a problem that there is a danger of receiving an electric shock through Cv and Cw. In addition, there is a problem that a large amount of leakage current flows through the ground terminal E and does not conform to regulations such as JIS-T1002 and UL1283. Also, R1, S1, T1 of the three-phase AC power supply 5 and inputs R2, S2,
Since the same current as the above-mentioned leakage current flows through the zero-phase current transformer 7 of the earth leakage breaker 6 provided between T2, the tripping coil 9 is operated by the amplifying unit 8 to cut off the circuit. Since the earth leakage breaker 6 generally has an operating current of 30 to 100 mA, the switching frequency of the power converter 2 is high and the load 3
There is a problem in that the larger the floating capacitance of the circuit breaker, the more the leakage breaker 6 malfunctions due to the high-frequency leakage current.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and a human body is required for an electric device having a high-frequency switching power converter in a housing and a load having a stray capacitance connected thereto. It is an object of the present invention to obtain an electric shock prevention circuit in an electric device for reducing a voltage of a housing with respect to a ground when contact is made.

[0009]

According to a first aspect of the present invention, there is provided an electric device for preventing electric shock in an electric appliance, comprising:
The voltage between the ground line on the side and the output line on the output side of the power converter is inverted, and the current flowing through the capacitor connected between the inverted output and the housing is opposite to the leakage current flowing through the floating capacitance of the load. The same current value is used in each direction, and the sum of the two currents becomes zero to reduce the voltage of the housing with respect to the ground, thereby preventing electric shock.

According to a second aspect of the present invention, there is provided an electric shock prevention circuit for controlling an electric potential of an input of a power conversion device such that a sum of voltages output from the power conversion device is equal to a potential of a ground line of an AC power supply. Then, the sum of the currents flowing from the output to the housing through the stray capacitance becomes zero to reduce the voltage of the housing with respect to the ground, thereby preventing electric shock.

According to a third aspect of the present invention, there is provided an electric shock prevention circuit for an electric appliance, comprising: a current flowing from an output line on the output side of a power converter to a housing through a stray capacitance to a ground line on an input side of the power converter. In this case, the voltage of the housing with respect to the ground is reduced by returning to the power conversion device through a capacitor connected between the housing and the housing, thereby preventing an electric shock.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electric shock prevention circuit in an electric device according to the present invention is an electric device 4 including a power converter 2 for switching at a high frequency in a housing 1 and a load 3 having a stray capacitance connected thereto. In the first and second embodiments, the voltage between the output of the power converter 2 and the ground line of the AC power supply 5 is inverted, and the current flowing through the capacitor connected between the inverted output and the housing is changed to the stray capacitance of the load. The same current value is used in the opposite direction to the leakage current flowing through the casing, and the sum of the two currents is made zero to reduce the voltage of the housing with respect to the ground, thereby preventing electric shock. In the third and fourth embodiments, the potential of the input of the power converter is controlled so that the sum of the voltage of the output of the power converter becomes the same as the potential of the ground line of the AC power supply. The sum of the currents flowing through the housing is reduced to zero to reduce the voltage of the housing with respect to the ground, thereby preventing electric shock. In the fifth embodiment, the current flowing from the output of the power converter to the housing through the stray capacitance returns to the power converter through the capacitor connected between the input ground line and the housing. Thus, the voltage of the housing with respect to the ground is reduced to prevent electric shock.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. <First Embodiment> An electric shock prevention circuit in an electric device applied to the electric device 4 shown in FIG. 1 is a first embodiment of the present invention. In the figure, the primary sides of transformers 46, 47, 48 are respectively connected between outputs U1, V1, W1 and the ground line S2 of the input of the power converter 2. Transformers 46, 47, 4
The voltage on the secondary side of the power conversion device 8 is inverted by connecting the polarity in reverse, and connected between the terminals X, Y, and Z and the ground line S2 of the input of the power conversion device 2, respectively. Capacitors C1, C2, and C3 are connected between the terminals X, Y, and Z and the housing 1, respectively.
The primary to secondary turns ratio of the transformers 46, 47, 48 is 1:
If it is set to 1, the capacitance of the capacitors C1, C2, C3 is set to the same value as the stray capacitances Cu, Cv, Cw. The electric shock prevention circuit in the electric apparatus according to the first embodiment is configured as described above.

The voltages of the outputs U1, V1, and W1 of the power converter 2 are switched between the potential 33 on the plus side P and the potential 34 on the minus side N in FIG. Change. That is, the low-frequency and high-frequency voltage changes overlap. This voltage is shown in FIG. The currents iu, iv, iw flowing through the stray capacitances Cu, Cv, Cw due to this voltage change are as shown in FIG. Transformers 46, 47, 48 according to the first embodiment
The voltages at the terminals X, Y, and Z inverted at (c) are shown in FIG.
The currents ix, iy, iz flowing through the capacitors C1, C2, or C3 connected to the terminals X, Y, Z are shown in (d) 45. This current has the same current value as 42 in (b) and the polarity is reversed. That is, when the currents of 42 in (b) and 45 in (d) are combined, the currents cancel each other and become zero as shown in (e) 46.

Leakage current ie flowing through ground terminal E of housing 1
Is the sum of iu, iv, iw, ix, iy, iz. i
u, iv, and iw have the same current as ix, iy, and iz, respectively, and have opposite polarities.
Is zero. In this way, the output voltages are inverted by the transformers 46, 47, and 48, and the stray capacitances Cu, Cv, Cw
The leakage current can be made zero by flowing a current having the same value as that of the current flowing in the opposite direction and having the opposite polarity. Therefore, even when the housing 1 is not grounded, the voltage of the housing 1 is zero, and no electric shock is caused by the contact of the human body with the housing, and an electric shock prevention circuit in the electric device can be obtained.

In this embodiment, a single-phase transformer 46,
Although 47 and 48 were used, the same effect can be obtained by using a three-phase transformer. In addition, since low-frequency and high-frequency currents flow simultaneously in these transformers, the degree of coupling between the primary and the secondary is high, and good results are obtained with good high-frequency characteristics. Specifically, a transformer in which a primary and a secondary are wound close to a ferrite core is practical. The capacitors 17 and 18 are connected to the diodes 12 and 13 of the power converter 2 of FIG. 1, respectively.
Are connected in parallel, the effect of the electric shock prevention circuit in the electric equipment is enhanced.

As described above, the electric shock prevention circuit in the electric device according to the present invention can reduce the leakage current to zero with a simple configuration using a transformer and a capacitor, and the voltage of the housing can be reduced even when the housing is not grounded. This is an excellent effect that no electric shock is caused by contact of the housing with the human body.

<Second Embodiment> An electric shock prevention circuit in an electric device applied to the electric device 4 shown in FIG. 2 is a second embodiment of the present invention. In the figure, one of the resistors Ru, Rv, Rw is connected to the outputs U1, V1, W1, respectively, and the other is connected to the negative input terminal 27 of the amplifier 26. Amplifier 2
6 is connected between the output 50 and the negative input terminal 27. The positive input terminal 28 of the amplifier 26 is connected to the input ground line S2 of the power converter 2. A capacitor Co is connected between the output 50 of the amplifier 26 and the housing 1. The resistances Ru, Rv,
When Rw and Ro have the same value, the capacitance of the capacitor Co is set to the same value as the stray capacitances Cu, Cv and Cw. The electric shock prevention circuit in the electric device of the second embodiment is configured as described above.

The voltages of the outputs U1, V1, and W1 of the power conversion device 2 are switched between the potential 33 on the positive side P and the potential 34 on the negative side N in FIG. Change. That is, the low-frequency and high-frequency voltage changes overlap. This voltage is shown in FIG. The currents iu, iv, iw flowing through the stray capacitances Cu, Cv, Cw due to this voltage change are as shown in FIG. The output voltage Vo inverted by the amplifier 26 according to the second embodiment is shown in FIG. The current io flowing through the capacitor Co connected to the voltage 44 is shown in (d) 45. This current has the same current value as 42 in (b) and the polarity is reversed. That is, when the currents of 42 in (b) and 45 in (d) are combined, the currents cancel each other and become zero as shown in (e) 46.

Leakage current ie flowing through ground terminal E of housing 1
Are the currents iu, iv, flowing through the stray capacitances Cu, Cv, Cw.
This is the sum of iw and the current io flowing through the capacitor Co. Since the same current has the opposite polarity, the leakage current ie obtained by summing all of them is zero. As described above, the output voltage is inverted by the amplifier 26, and a current having the same value as the current flowing through the stray capacitances Cu, Cv, and Cw and having the opposite polarity flows, thereby making the leakage current zero. Therefore, even when the housing 1 is not grounded, the voltage of the housing 1 is zero, and no electric shock is caused by the contact of the human body with the housing, and an electric shock prevention circuit in the electric device can be obtained.

In this embodiment, the resistors Ru, Rv, Rw
, And one amplifier 26 and one capacitor C
However, the same effect can be obtained by using three circuits of the amplifier 26 and the capacitor Co for each of the resistors Ru, Rv, and Rw.

As described above, the electric shock prevention circuit in the electric equipment according to the present invention does not use a magnetic material such as an inductance or a transformer, and reduces the voltage of the housing with respect to the ground to zero with a simple configuration using a resistor, an amplifier and a capacitor. Therefore, there is an excellent effect that the magnetic material is not saturated, and a compact, lightweight, and inexpensive product can be obtained.

Third Embodiment An electric shock prevention circuit in an electric device applied to the electric device 4 shown in FIG. 3 is a third embodiment of the present invention. In the figure, a common mode choke coil 29 is provided between the three-phase AC power supply 5 and the power converter 2.
And the capacitors 30, 31, and 32 are connected between the inputs R2, S2, and T2 of the power converter 2. Resistance Ru, Rv, R
One of w is connected to U1, V1, and W1, respectively, and the other is connected to the negative input terminal 27 of the amplifier 26. Amplifier 2
6, a resistor Rp is connected between the output 50 and the negative input terminal 27. The resistance Rp is a value sufficiently larger than the resistances Ru, Rv, and Rw. For example, a resistance value that is 10 times is selected. The positive input terminal 28 of the amplifier 26 is connected to the ground line S1 of the three-phase AC power supply 5. The output 50 of the amplifier 26 is connected to the ground line S2 of the input of the power converter 2. The electric shock prevention circuit in the electric device according to the third embodiment is configured as described above.

The voltages of the outputs U1, V1, and W1 of the power conversion device 2 are switched between the potential 33 on the plus side P and the potential 34 on the minus side N in FIG. Change. That is, the low-frequency and high-frequency voltage changes overlap. The voltage Vp of the output 50 inverted and amplified by the amplifier 26 according to the third embodiment is converted into a power so that the sum of the voltages of the outputs U1, V1, and W1 becomes the potential of the ground line S1 of the three-phase AC power supply 5, that is, zero. The potential of the input ground line S2 of the device 2 is controlled. This result output U
Since the sum of the voltages of 1, V1, and W1 becomes zero, the current i flowing through the stray capacitances Cu, Cv, and Cw due to this voltage change
The sum of u, iv and iw becomes zero. The leakage current ie flowing through the ground terminal E of the housing 1 is the sum of the currents iu, iv and iw flowing through the stray capacitances Cu, Cv and Cw. Since this current is zero, the leakage current ie is zero. Therefore, even when the housing 1 is not grounded, the voltage of the housing 1 is zero, and no electric shock is caused by the contact of the human body with the housing, and an electric shock prevention circuit in the electric device can be obtained.

As described above, the output voltage is inverted and amplified by the amplifier 26, and the potential of the ground line at the input of the power converter is controlled by the inverted and amplified output. Thus, an electric shock prevention circuit in an electric device capable of preventing the occurrence of electric shock can be obtained.

Further, by connecting the capacitors 17 and 18 to the diodes 12 and 13 connected to the input S2, the outputs U1, V1 and W1
It is easy to control the sum of the voltages to zero. The same effect can be obtained even if a capacitor is connected in parallel with the diodes 10, 11, 14, and 15. Further, by inserting a capacitor 51 between the output 50 of the amplifier 26 and the ground line S2 of the input of the power converter 2 and passing only a high-frequency current, the voltage of the output U1, V1, W1 of the power converter 2 is reduced. Only high frequency components are controlled to zero, and stray capacitances Cu, Cv,
The sum of the high frequency components of the currents iu, iv, iw flowing through Cw is set to zero. The leakage current of the low frequency component is 4 in FIG.
As shown in FIG. 3, the total leakage current is also small.
Further, there is an effect that the common mode choke coil 29 does not saturate with a low frequency component, and the power consumption of the amplifier 26 can be reduced.

The electric shock prevention circuit in the electric equipment applied to the electric equipment 4 shown in FIG. 3 has a structure in which the load 3 is installed outside the housing 1 and is grounded separately from the housing 1.
Since the sum of the voltages of the outputs U1, V1, and W1 becomes zero, the currents iu, i flowing through the stray capacitances Cu, Cv, and Cw of the load 3
The sum of v and iw is zero. Therefore, when the load 3 is not grounded, there is no electric shock even if a human body comes into contact with the case of the load 3.

As described above, the electric shock prevention circuit in the electric equipment according to the present invention can reduce the voltage of the housing with respect to the ground with a simple configuration including the common mode choke coil, the capacitor, the resistor, and the amplifier, and is small, light, and low. It has an excellent effect of obtaining a price.

<Fourth Embodiment> An electric shock prevention circuit in an electric apparatus shown in FIG. 4 is a fourth embodiment of the present invention. In the figure, a common mode choke coil 52 is connected between the three-phase AC power supply 5 and the power converter 2, and capacitors 30, 31, and 32 are connected between the inputs R2, S2, and T2 of the power converter 2. One of the resistors Ru, Rv, and Rw is set to U
1, V1 and W1 and the other is connected to the negative input terminal 27 of the amplifier 26. A resistor Rp is connected between the output 50 of the amplifier 26 and the negative input terminal 27. The resistance Rp is the resistance R
u, Rv, and Rw are values that are sufficiently larger. For example, a resistance value that is 10 times is selected. The positive input terminal 28 of the amplifier 26 is connected to the ground line S1 of the three-phase AC power supply 5. The auxiliary winding 53 of the common mode choke coil 52 is connected between the output 50 of the amplifier 26 and the ground line S1 of the three-phase AC power supply 5. The electric shock prevention circuit in the electric apparatus according to the fourth embodiment is configured as described above.

The voltage Vp of the output 50 inverted and amplified by the amplifier 26 according to the fourth embodiment is equal to the output U1, V1, W1
Of the input of the power conversion device 2 so that the sum of the voltages of
2 is controlled. As a result, the sum of the voltages of the outputs U1, V1, and W1 becomes zero, and the sum of the currents iu, iv, and iw flowing through the stray capacitances Cu, Cv, and Cw becomes zero due to this voltage change. The leakage current ie flowing to the ground terminal E of the housing 1 is the current iu, i flowing to the stray capacitance Cu, Cv, Cw.
This is the sum of v and iw, and since this current is zero, the leakage current ie is zero. Therefore, even when the housing 1 is not grounded, the voltage of the housing 1 is zero, and no electric shock is caused by the contact of the human body with the housing, and an electric shock prevention circuit in the electric device can be obtained.

As described above, the output voltage of the power converter is inverted and amplified by the amplifier 26, and the potential of the ground line at the input of the power converter is controlled by the inverted and amplified output, thereby reducing the voltage of the housing with respect to the ground. An electric shock prevention circuit in an electric device that can perform the operation is obtained.

Further, by inserting a capacitor 51 between the output 50 of the amplifier 26 and the ground line S1 of the three-phase AC power supply 5 and passing only a high-frequency current, the output U1, V1, W1 of the power converter 2 is Only the high frequency components of the voltage are controlled to zero, and the currents iu, i flowing through the stray capacitances Cu, Cv, Cw
The sum of the high frequency components of v and iw is set to zero. Since the leakage current of the low frequency component is small as shown at 43 in FIG. 8B, the overall leakage current is also small. Also, there is an effect that the common mode choke coil 52 is not saturated with a low frequency component. Also, the common mode choke coil 5
By reducing the number of turns of the second auxiliary winding 53 from that of the other windings, for example, by reducing the number of turns, the voltage of the output voltage Vp of the amplifier 26 may be low, and an effect that an amplifier made of a semiconductor can be easily formed. There is.

The electric shock prevention circuit in the electric equipment applied to the electric equipment 4 shown in FIG. 4 has a structure in which the load 3 is installed outside the housing 1 and is grounded separately from the housing 1.
Since the sum of the voltages of the outputs U1, V1, and W1 becomes zero, the currents iu, i flowing through the stray capacitances Cu, Cv, and Cw of the load 3
The sum of v and iw is zero. Therefore, when the load 3 is not grounded, there is no electric shock even if a human body comes into contact with the case of the load 3.

As described above, the electric shock prevention circuit in the electric equipment according to the present invention can reduce the voltage of the housing with respect to the ground with a simple configuration including the common mode choke coil, the capacitor, the resistor, and the amplifier, and is small, light, and low. It has an excellent effect of obtaining a price.

Fifth Embodiment An electric shock prevention circuit in an electric device applied to the electric device 4 shown in FIG. 5 is a fifth embodiment of the present invention. In the figure, a common mode choke coil 29 is provided between the three-phase AC power supply 5 and the power converter 2.
And the capacitors 30, 31, and 32 are connected between the inputs R2, S2, and T2 of the power converter 2. Also, a capacitor 37 is provided between the input ground line S2 of the power converter 2 and the housing 1.
Connect. The capacitor 37 has a stray capacitance Cu, Cv, C
The value is set to a value sufficiently larger than the capacitance of w. For example, 0.
Choose between 1 and 1 μF. The electric shock prevention circuit in the electric device according to the fifth embodiment is configured as described above.

The ground line S2 at the input of the power converter 2 has a ground potential at a low frequency because the three-phase AC power supply S1 is grounded. Therefore, even if S2 and the housing 1 grounded by the ground terminal E are connected by the capacitor 37, they have almost the same potential and almost no low-frequency current flows. Further, since the power converter 2 is insulated from the housing 1, the outputs U1, V1, W1 are provided for the inputs R2, S2, T2 of the power converter 2.
Of the stray capacitance Cu, Cv, C
The currents iu, iv, iw flowing through w flow through the capacitor 37 to the input S2 of the power converter 2. Power converter 2
Inputs R2, S2, T2 are capacitors 30, 31, 32
Are the same in terms of high frequency. Since the capacitance of the capacitor 37 is set to a value sufficiently larger than the capacitance of the stray capacitances Cu, Cv, Cw, the stray capacitances Cu, Cv, Cw
The currents iu, iv, iw flowing through w almost flow through the capacitor 37 as the current is and flow inside the power converter 2.

Further, by connecting the capacitors 17 and 18 to the diodes 12 and 13 connected to the input S2, the current is flowing through the capacitor 37 during the phase in which the diodes 12 and 13 are not conducting is increased. , And the effect of reducing the voltage of the housing with respect to the ground is enhanced. The same effect can be obtained even if a capacitor is connected in parallel with the diodes 10, 11, 14, and 15.

The capacitor 37 has stray capacitances Cu, Cv, C
Since the capacitance is set to be relatively large as compared with w, the terminal voltage due to the current is is small. Therefore, a small amount of current flows to the three-phase AC power supply 5 due to the inductance of the common mode choke coil 29. Further, as described above, the low-frequency current flowing through the capacitor 37 is small, and the current flowing through the high-frequency stray capacitances Cu, Cv, Cw is
Since it returns to the power converter 2 through 7, 17, and 18, the leakage current ie flowing to the ground terminal E is small. Therefore, even when the housing 1 is not grounded, the voltage of the housing 1 with respect to the ground is low, and no electric shock is caused by contact of the body with the housing, so that an electric shock prevention circuit in the electric device can be obtained.

As described above, the electric shock prevention circuit in the electric equipment according to the present invention can reduce the voltage of the housing with respect to the ground with a simple configuration using the common mode choke coil and the capacitor. It has an excellent effect of being obtained.

The first to fifth embodiments described above have three
As shown in the electric shock prevention circuit in electric equipment for phase alternating current,
The same effect can be achieved with a similar circuit even in an electric shock prevention circuit in an electric device for single-phase AC or single-phase three-wire AC.

[0041]

Since the present invention is configured as described above, it has the following effects.
The electric shock prevention circuit in the electric equipment of the first and second embodiments connects a load having a stray capacitance to a power converter that switches at a high frequency by flowing a current having the same value as the current flowing through the stray capacitance and having the opposite polarity. The voltage of the housing with respect to the grounding of the electric device can be reduced, and even when the housing is not grounded, there is no possibility that a human body touches the housing and receives an electric shock. In addition, the voltage of the housing with respect to the ground can be reduced with a simple configuration including a transformer and a capacitor or a resistor, an amplifier, and a capacitor.

The electric shock prevention circuit in the electric equipment of the third and fourth embodiments controls the input potential of the power converter so that the sum of the output voltages of the power converter becomes equal to the potential of the ground line of the AC power supply. Therefore, the leakage current flowing from the output to the stray capacitance can be reduced, and even if the housing is not grounded, the human body does not come into contact with the housing to receive an electric shock. Also, even if the load is installed outside the housing and is not connected to the housing, the case of the load 3 does not come into contact with the case of the human body and does not receive an electric shock. In addition, the voltage of the housing with respect to the ground can be reduced with a simple configuration including a common mode choke coil and a capacitor, and a resistor and an amplifier.

In the electric shock prevention circuit in the electric equipment of the fifth embodiment, the current flowing from the output of the power converter to the housing through the stray capacitance is connected between the input ground line of the power converter and the housing. Since the power returns to the power conversion device through the capacitor, the voltage of the housing with respect to the ground can be reduced. Even when the housing is not grounded, the housing does not come into contact with the human body and does not cause an electric shock. Further, the voltage of the housing with respect to the ground can be reduced with a simple configuration using the common mode choke coil and the capacitor, and there is an effect that a compact, lightweight, and low-cost one can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an electric shock prevention circuit in an electric device according to a first embodiment.

FIG. 2 is a circuit diagram illustrating an electric shock prevention circuit in an electric device according to a second embodiment.

FIG. 3 is a circuit diagram showing an electric shock prevention circuit in an electric device according to a third embodiment.

FIG. 4 is a circuit diagram illustrating an electric shock prevention circuit in an electric device according to a fourth embodiment.

FIG. 5 is a circuit diagram illustrating an electric shock prevention circuit in an electric device according to a fifth embodiment.

FIG. 6 is a circuit diagram for explaining the operation of a conventional electric device.

7 is a waveform diagram of each section for explaining the operation of the conventional electric device and the embodiment of FIG.

8 is a waveform diagram of each part for explaining the operation of the conventional electric device and the embodiment of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Power converter 3 Load 4 Electric equipment 5 AC power supply 6 Leakage breaker 7 Zero-phase current transformer 8 Amplification part 9 Tripping coil 10, 11, 12 Diode 13, 14, 15 Diode 16, 17, 18 Capacitor 20, 21, 22 Switching element 23, 24, 25 Switching element 26 Amplifier 27 Negative input terminal 28 Positive input terminal 29, 52 Common mode choke coil 30, 31, 32 Capacitor 37, 51 Capacitor 46, 47, 48 Transformer 53 Auxiliary winding Line C1, C2, C3 Capacitor Co Capacitor E Ground terminal Ru, Rv, Rw Resistance Ro, Rp Resistance R2, S2, T2 Input U1, V1, W1 Output U2, V2, W2 Input terminal Vo, Vp Output voltage

Claims (3)

(57) [Claims] An AC power supply having a power converter and a load in a housing, one of which is grounded, is input to the power converter, and a desired voltage is applied to a load connected to an output of the power converter. in electrical equipment which outputs a waveform, the input side of the ground line and the power converter of the power converter
Invert the voltage between the output line of the output side and the power conversion
Stray capacitance existing between the output line on the output side of the device and the housing
And by connecting the capacitors to flow total equivalent current of the current which leaks from the floating capacitance between the input side of the load existing between the housing between the housing and the inverted output, a housing to ground An electric shock prevention circuit in an electric device, characterized by reducing a voltage of the electric shock. 2. A power conversion device having a power conversion device in a housing, one of which is grounded, is input to the power conversion device, and a desired voltage waveform is output to a load connected to an output of the power conversion device. In an electrical device, a common mode choke coil is connected between an AC power supply and an input of a power converter, and a capacitor is connected between input lines of the power converter, and a voltage of an output of the power converter is connected. And the voltage difference between the ground line of the AC power supply is inverted and amplified, and the potential of the input ground line of the power conversion device is controlled by the inverted amplified output, thereby obtaining An electric shock prevention circuit in an electric device, characterized in that the electric shock is reduced. 3. An AC power supply having a power converter and a load in a housing, one of which is grounded, is input to the power converter, and a desired voltage is applied to a load connected to an output of the power converter. in electrical equipment which outputs a waveform, and a capacitor between the input of the AC power source and the power conversion device further before between the ground line and the housing of the input of the power converter
The power converter exists between the output line on the output side of the power converter and the housing.
Between the input side of the load and the housing
An electric shock prevention circuit in an electric device, wherein a capacitor having a capacitance sufficiently larger than a stray capacitance is connected to reduce a voltage of a housing with respect to a ground.