JPH0965564A - Electric shock preventive circuit in electric equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric shock preventive circuit which reduces the voltage to earth of a case when a human body touches an electric equipment which has in the case a power converter that conducts switching operations at high frequencies and a load that, being connected to the power converter, has a stray capacitance. SOLUTION: An electric equipment has a power converter and a load connected to the power converter in a box. In such an electric equipment, the primary sides of transformers 46, 47, 48 are connected between outputs U1, V1, W1 and an input earth line S2 of the power converter 2 and then the voltages at the secondary sides of the transformers are inversed. The secondary sides of the transformers to which capacitors C1, C2, C3 are serially connected respectively are connected between the input earth line S2 of the power converter 2 and the case. The currents in the capacitors C1, C2, C3 flow in the opposite direction to leakage currents in stray capacitances Cu, Cv, Cw of the load but the absolute values are the same as those of the leakage currents. Since the sum of the currents in the capacitors C1, C2, C3 and the leakage currents in the stray capacitances Cu, Cv, Cw becomes zero, the voltage to earth of the case can be reduced and thereby an electric shock can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reduces the voltage generated in the housing due to stray capacitance from the load of a power conversion device provided in the housing of an electric device for inputting an AC power source, and the housing is grounded. The present invention relates to a circuit that prevents electric shock to the human body even if it is not installed.

[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 composed of a conductor such as an iron plate and having the same electric potential and in which electrical parts are attached and housed. The electric device 4 is a three-phase AC power supply R1, S1 in which the S phase of the AC power supply 5 is grounded,
The earth leakage breaker 6 is connected to T1, and the input R of the power converter 2
2, S2, T2. The power conversion device 2 generally rectifies an AC voltage, converts it into a DC voltage, and then 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 and becomes a constant DC voltage. Switching element 20-
25 is switched at a high frequency by, for example, PWM control (pulse width modulation control) and outputs a low-frequency waveform such as a 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 PWM control,
It is driven by a low frequency sinusoidal voltage. The load 3 is attached to the housing 1, and the housing 1 is normally connected to the ground terminal E and grounded. The conventional electric device 4 is configured as described above.

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

FIG. 7 is a waveform of each part of the conventional electric equipment 4 of FIG. 30 in (a) is R1-S1 of the three-phase AC power supply 5.
It is a voltage waveform between. Similarly, 31 is 32 between S1 and T1.
Is the voltage waveform of S1. Since the S1 of the three-phase AC power supply 5 is grounded, the voltage of S1 of 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 potential on the positive side P, and 34 is a potential on the negative side N. Reference numeral 35 indicates an intermediate voltage between P and N. The voltage between P and N is constant due to the large-capacity capacitor 16, but the operating voltage with respect to the ground of the power converter 2 becomes a distorted low-frequency AC voltage like 35 due to the conducting phase of the diodes 10 to 15. . Switching element 2
Each of 0 to 25 switches the output to P potential or N potential at a high frequency by switching. For example, if the switching element 20 is turned on, the output U1
Has a P potential, and when the switching element 21 is turned ON, the output U1 has an N potential. Therefore, the potential of the output U1 changes at a high frequency (carrier frequency) of PWM control.
As described above, in the outputs U1, V1, and W1, 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 the switching of 25. When the line voltage of the three-phase AC power supply 5 is 200 V, P and N
The voltage difference is about 270V.

FIG. 8 shows an enlarged view of the portion 36 in FIG. 7 (b). (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. This waveform 40 has, for example, a carrier frequency of 15
It becomes an almost rectangular wave of KHz. Since the voltage change is steep at the portion 41 of the voltage waveform 40 at the time of switching, the current waveform of the leakage current iu flowing in the stray capacitance Cu is the ground terminal E.
Is grounded, the peak is 1 as shown in (b) 42.
A large leakage current of up to 2 A or more flows. Since the portion 36 in FIG. 7B is a period in which the potentials of P and N are rising, the portion 43 in FIG. 8B is the stray capacitance Cu.
Although a positive current flows as a current waveform of the leakage current iu flowing through, the leakage current is small because the voltage change is slow. Therefore, most of the leakage current is from the switching element 20 to
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, the voltage of the waveform 40 in FIG. 8A causes the stray capacitances Cu, Cv, C when the human body touches.
There was a risk of electric shock because the current of (b) flows through w in the worst case.

<Documents Related to Conventional Technology> Documents related to conventional technology are as follows. 1. Ogasawara, Fujita, Akagi: "Modeling and theoretical analysis of high-frequency leakage current generated by voltage-type PWM inverter", IEEJ Transactions D (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", IEEJ workshop
Technical Committee on Semiconductor Power Conversion SPC-95-31, June 9, 1995 3. Published Utility Model Bulletin Sho 62-88484 "Electrical Leakage Prevention Device"

[0007]

Since the conventional electric equipment 4 is constructed as described above, the ground wire is disconnected or cut when the housing 1 is not grounded or the grounding is incomplete. In case of high frequency leakage current stray capacitance Cu,
There is a problem that there is a risk of being electrocuted through Cv and Cw. In addition, there is a problem that a large amount of leakage current flows through the ground terminal E, which does not comply with regulations such as JIS-T1002 and UL1283. In addition, R1, S1 and T1 of the three-phase AC power supply 5 and inputs R2 and S2 of the power conversion device 2
Since the same current as the leakage current flows in the zero-phase current transformer 7 of the earth leakage breaker 6 provided between the T2 and T2, the tripping coil 9 is operated by the amplifying unit 8 to shut off the circuit. Since the leakage current 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 that the leakage current breaker 6 malfunctions due to the high-frequency leakage current as the stray capacitance of the leakage current is larger.

The present invention has been made in order to solve the above-mentioned problems, and a human body is attached to an electric device equipped with a power conversion device for switching at high frequency in a housing and a load having a stray capacitance connected to the power conversion device. An object of the present invention is to obtain an electric shock prevention circuit in an electric device for reducing the voltage of the housing with respect to the ground when it comes into contact.

[0009]

According to a first aspect of the present invention, there is provided an electric shock preventive circuit in an electric device, which inverts a voltage between an input ground line and an output of a power conversion device, and the inverted output and a housing. The current flowing in the capacitor connected between the and the leakage current flowing in the stray capacitance of the load is made the same current value in the opposite direction, the total of both currents becomes zero, and the voltage of the casing with respect to ground is reduced, It prevents electric shock.

In the electric shock preventive circuit in the electric device according to the second aspect of the present invention, the potential of the input of the power converter is controlled so that the sum of the voltages of the outputs of the power converter is the same as the potential of the ground line of the AC power supply. The electric current is prevented by reducing the voltage of the casing with respect to the ground by making the total of the currents flowing from the output to the casing through the stray capacitance to zero.

According to another aspect of the present invention, in an electric shock preventive circuit in an electric device, a current flowing from an output of a power converter through a stray capacitance to a housing is applied between a ground wire of an input of the power converter and the housing. By passing through the connected capacitor and returning to the power conversion device, the voltage of the housing with respect to the ground is reduced and electric shock is prevented.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An electric shock preventive circuit in an electric device according to the present invention is an electric device 4 including a power converter 2 for switching at high frequency in a housing 1 and a load 3 having a stray capacitance connected to the power converter 2. In the first and second embodiments, the voltage between the output of the power converter 2 and the ground wire of the AC power supply 5 is inverted, and the current flowing in the capacitor connected between the inverted output and the housing is changed to the stray capacitance of the load. The electric current is prevented by reducing the voltage of the casing with respect to the ground by setting the same current value in the opposite direction as the leakage current flowing through the device so that the total of both currents becomes zero. In the third and fourth embodiments, the input potential of the power conversion device is controlled so that the sum of the output voltages of the power conversion device becomes the same as the potential of the ground line of the AC power supply, and the output is passed through the stray capacitance. The electric current is prevented by reducing the voltage of the casing with respect to the ground by making the total current flowing through the casing zero. Further, in the fifth embodiment, the current flowing from the output of the power converter through the stray capacitance to the housing returns to the power converter through the capacitor connected between the ground line of the input of the power converter and the housing. In this way, the voltage of the housing with respect to the ground is reduced to prevent electric shock.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> An electric shock preventive 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 the transformers 46, 47, 48 are connected between the outputs U1, V1, W1 and the ground line S2 of the input of the power conversion device 2, respectively. Transformers 46, 47, 4
The voltage on the secondary side of 8 is inverted by connecting the polarities 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 turns ratio of the primary and secondary of the transformers 46, 47, 48 is 1:
If set to 1, the electrostatic capacitances of the capacitors C1, C2, C3 are set to the same values as the stray capacitances Cu, Cv, Cw. The electric shock prevention circuit in the electric device of the first 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 positive side P potential 33 and the negative side N potential 34 of FIG. 7B by switching with high frequency PWM control. 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 (b). The transformers 46, 47, 48 according to the first embodiment.
The voltages of the terminals X, Y, and Z which are inverted by (4) are shown in (c) 44.
The currents ix, iy, iz flowing through the capacitors C1, C2, or C3 connected to the terminals X, Y, Z are indicated by (d) 45. This current has the same current value as 42 in (b) but the polarity is reversed. That is, when the currents of 42 in (b) and 45 in (d) are combined, the currents cancel each other out to zero as shown in (e) 46.

Leakage current ie flowing through the ground terminal E of the housing 1
Is the sum of iu, iv, iw, ix, iy, iz. i
Since u, iv, and iw have the same currents as ix, yy, and iz, respectively, and their polarities are opposite, leakage current ie summing all of them.
Is zero. In this way, the output voltages are inverted by the transformers 46, 47, 48, and the stray capacitances Cu, Cv, Cw are
The leakage current can be reduced to zero by flowing a current having the same value as the current flowing in the opposite polarity. Therefore, even if the casing 1 is not grounded, the voltage of the casing 1 is zero, the human body does not come into contact with the casing to receive an electric shock, and an electric shock prevention circuit in an electric device can be obtained.

Further, in this embodiment, the single-phase transformer 46,
Although 47 and 48 are used, the same effect can be obtained by using a three-phase transformer. Further, since low frequency and high frequency flow simultaneously in these transformers, the degree of coupling between the primary and the secondary is high, and good results can be 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. Further, the diodes 12 and 13 of the power conversion device 2 of FIG.
If these are connected in parallel, the effect of the electric shock prevention circuit in electric equipment will be enhanced.

As described above, the electric shock preventive circuit in the electric equipment according to the present invention can reduce the leakage current to zero with a simple structure of the transformer and the capacitor, and the voltage of the case is not changed even if the case is not grounded. It is zero, and an excellent effect that the human body does not come into contact with the housing and receive an electric shock is obtained.

<Second Embodiment> An electric shock preventive 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 and Rw is connected to the outputs U1, V1 and W1, respectively, and the other is all connected to the negative input terminal 27 of the amplifier 26. Amplifier 2
A resistor Ro is connected between the output 50 of 6 and the negative input terminal 27. The positive input terminal 28 of the amplifier 26 is connected to the ground line S2 at the input of the power conversion device 2. A capacitor Co is connected between the output 50 of the amplifier 26 and the housing 1. 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 of FIG. 7 (b) by switching with high frequency PWM control. 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 (b). The output voltage Vo inverted by the amplifier 26 according to the second embodiment is shown in (c) 44. The current io flowing in the capacitor Co connected to this voltage 44 is shown in (d) 45. This current has the same current value as 42 in (b) but the polarity is reversed. That is, when the currents of 42 in (b) and 45 in (d) are combined, the currents cancel each other out to zero as shown in (e) 46.

Leakage current ie flowing through the ground terminal E of the housing 1
Are currents iu, iv flowing in the stray capacitances Cu, Cv, Cw,
It is the sum of iw and the current io flowing through the capacitor Co. Since the same current has the opposite polarity, the total leakage current ie is zero. In this way, 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 but having the opposite polarity can be made to flow and the leakage current can be made zero. Therefore, even if the casing 1 is not grounded, the voltage of the casing 1 is zero, the human body does not come into contact with the casing to receive an electric shock, and an electric shock prevention circuit in an electric device can be obtained.

Further, in this embodiment, the resistors Ru, Rv, Rw are used.
The currents of the two capacitors are summed to form 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 preventive circuit in the electric device according to the present invention does not use a magnetic substance such as an inductance or a transformer, and makes the voltage of the case to ground zero with a simple structure of a resistor, an amplifier and a capacitor. Therefore, it is possible to obtain a small size, a light weight, and a low price without the magnetic substance being saturated.

<Third Embodiment> An electric shock preventive 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 conversion device 2.
And capacitors 30, 31, 32 are connected between the inputs R2, S2, 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 all connected to the negative input terminal 27 of the amplifier 26. Amplifier 2
A resistor Rp is connected between the output 50 of 6 and the negative input terminal 27. The resistance Rp has a value sufficiently larger than the resistances Ru, Rv, and Rw. For example, select a resistance value of 10 times. 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 at the input of the power conversion device 2. The electric shock prevention circuit in the electric device of 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 positive side P potential 33 and the negative side N potential 34 of FIG. 7B by switching with high frequency PWM control. Change. That is, the low frequency and high frequency voltage changes overlap. The voltage Vp of the output 50, which is inverted and amplified by the amplifier 26 according to the third embodiment, is converted 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. Control the potential of the ground line S2 at the input of the device 2. 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, iw flowing through the stray capacitances Cu, Cv, Cw. Since this current is zero, the leakage current ie is zero. Therefore, even if the casing 1 is not grounded, the voltage of the casing 1 is zero, the human body does not come into contact with the casing to receive an electric shock, and an electric shock prevention circuit in an electric device can be obtained.

In this way, the output voltage is inverted and amplified by the amplifier 26, and the potential of the ground line of the input of the power converter is controlled by the inverted and amplified output. An electric shock prevention circuit in an electric device capable of preventing the electric shock is 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 V1 are output by the output of the amplifier 26 even during the period in which the diodes 12 and 13 are not conducting. W1
Makes it easy to control the sum of the voltages at zero. Also, the same effect can be obtained by connecting capacitors in parallel to the diodes 10, 11, 14, and 15. Further, by inserting the capacitor 51 between the output 50 of the amplifier 26 and the ground line S2 of the input of the power conversion device 2 and passing only the high frequency current, the voltages of the outputs U1, V1 and W1 of the power conversion device 2 are changed. Stray capacitance Cu, Cv,
The sum of the high frequency components of the currents iu, iv, and iw flowing in Cw is set to zero. The leakage current of the low frequency component is 4 in Fig. 8 (b).
As shown in 3, the total leakage current is also small.
Further, the common mode choke coil 29 is not saturated with the low frequency component, and the power consumption of the amplifier 26 can be reduced.

Further, in the electric shock preventive circuit in the electric device applied to the electric device 4 shown in FIG. 3, even if 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, W1 becomes zero, the currents iu, i flowing in the stray capacitances Cu, Cv, Cw of the load 3
The sum of v and iw is zero. Therefore, if the load 3 is not grounded, there is no electric shock even if the human body contacts the case of the load 3.

As described above, the electric shock preventive circuit in the electric device according to the present invention can reduce the voltage of the housing with respect to the ground with a simple structure including the common mode choke coil, the capacitor, the resistor and the amplifier, and is small, lightweight and low in size. It has an excellent effect of obtaining a priced product.

<Fourth Embodiment> The electric shock preventive circuit in the electric equipment 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 conversion device 2, and capacitors 30, 31, 32 are connected between inputs R2, S2, T2 of the power conversion device 2. One of the resistors Ru, Rv, and Rw is U, respectively.
1, V1, W1 and the other are all 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. Resistance Rp is resistance R
The value is sufficiently larger than u, Rv, and Rw. For example, select a resistance value of 10 times. 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 wire S1 of the three-phase AC power supply 5. The electric shock prevention circuit in the electric device of 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 the outputs U1, V1 and W1.
So that the sum of the voltages of the two becomes equal to the potential of the ground line S1 of the three-phase AC power supply 5, that is, zero, the ground line S of the input of the power conversion device 2.
Control the potential of 2. As a result, the sum of the voltages of the outputs U1, V1, W1 becomes zero, so that the total of the currents iu, iv, iw flowing through the stray capacitances Cu, Cv, Cw becomes zero due to this voltage change. The leakage current ie flowing through the ground terminal E of the housing 1 is the current iu, i flowing through the stray capacitances Cu, Cv, Cw.
It is the sum of v and iw, and since this current is zero, the leakage current ie is zero. Therefore, even if the casing 1 is not grounded, the voltage of the casing 1 is zero, the human body does not come into contact with the casing to receive an electric shock, and an electric shock prevention circuit in an electric device can be obtained.

In this way, 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 preventive circuit in an electric device 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 high-frequency current, the outputs U1, V1, W1 of the power conversion device 2 are changed. Only the high frequency components of the voltage are controlled to zero, and the currents iu, i flowing in the stray capacitances Cu, Cv, Cw are controlled.
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 indicated by 43 in FIG. 8B, the total leakage current is also small. Further, there is an effect that the common mode choke coil 52 will not be saturated with a low frequency component. Also, common mode choke coil 5
By reducing the number of turns of the second auxiliary winding 53 different from the number of turns of other windings, for example, the number of turns, the voltage of the output voltage Vp of the amplifier 26 may be low, and an effect that a semiconductor amplifier can be easily configured. There is.

Further, in the electric shock preventive circuit in the electric device applied to the electric device 4 shown in FIG. 4, even if 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, W1 becomes zero, the currents iu, i flowing in the stray capacitances Cu, Cv, Cw of the load 3
The sum of v and iw is zero. Therefore, if the load 3 is not grounded, there is no electric shock even if the human body contacts the case of the load 3.

As described above, the electric shock preventive circuit in the electric device according to the present invention can reduce the voltage of the housing with respect to the ground with a simple configuration of the common mode choke coil, the capacitor, the resistor and the amplifier, and is small, lightweight and low in size. It has an excellent effect of obtaining a priced product.

<Fifth Embodiment> An electric shock preventive 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 conversion device 2.
And capacitors 30, 31, 32 are connected between the inputs R2, S2, T2 of the power converter 2. Further, a capacitor 37 is provided between the ground line S2 of the input of the power conversion device 2 and the housing 1.
Connect. The capacitor 37 is a stray capacitance Cu, Cv, C
It is set to a value sufficiently larger than the capacitance of w. For example, 0.
Select from 1 to 1 μF. The electric shock prevention circuit in the electric device of the fifth embodiment is constructed as described above.

The ground line S2 of the input of the power converter 2 is at ground potential at low frequencies because S1 of the three-phase AC power source is grounded. Therefore, even if the capacitor 37 is connected between the S2 and the housing 1 grounded by the ground terminal E, almost no low-frequency current flows because of the same potential. Further, since the power conversion device 2 is insulated from the housing 1, the outputs U1, V1, W1 are corresponding to the inputs R2, S2, T2 of the power conversion device 2.
Of the stray capacitances Cu, Cv, C
The currents iu, iv, and iw flowing through w flow through the capacitor 37 to the input S2 of the power conversion device 2. Power converter 2
Inputs R2, S2, T2 are capacitors 30, 31, 32
Therefore, they have the same potential in terms of high frequency. Since the electrostatic capacitance of the capacitor 37 is set to a value sufficiently larger than the electrostatic capacitances of the stray capacitances Cu, Cv, Cw, the stray capacitances Cu, Cv, C
The currents iu, iv, and iw flowing through w almost flow through the capacitor 37 as the current is and flow inside the power conversion device 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 period when the diodes 12 and 13 are not conducting is converted into the power converter 2 To facilitate the flow to the DC voltage portion of the, and enhance the effect of reducing the voltage of the housing with respect to ground. Also, the same effect can be obtained by connecting capacitors in parallel to the diodes 10, 11, 14, and 15.

The capacitor 37 is a stray capacitance Cu, Cv, C.
Since the capacitance is set to be relatively larger than w, the terminal voltage due to the current is is small. Therefore, due to the inductance of the common mode choke coil 29, the current flowing to the three-phase AC power source 5 side is small. 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, and Cw is the capacitor 3
Since it returns to the power conversion device 2 through 7, 17, and 18, the leakage current ie flowing through 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 the human body does not come into contact with the housing to receive an electric shock, and an electric shock prevention circuit in an electric device can be obtained.

As described above, the electric shock preventive circuit in the electric device according to the present invention can reduce the voltage of the casing with respect to the ground with a simple structure of the common mode choke coil and the capacitor, and is small in size, light in weight and low in price. It has an excellent effect of being obtained.

The first to fifth embodiments described above are 3
Although it was shown in the electric shock prevention circuit in the electrical equipment for phase alternating current,
Even in an electric shock prevention circuit in an electric device for single-phase alternating current, single-phase three-wire alternating current, or the like, the same effect can be obtained with the same circuit.

[0041]

Since the present invention is configured as described above, it has the following effects.
The electric shock prevention circuits in the electric devices of the first and second embodiments connect a load having a stray capacitance to a power conversion device that switches at a high frequency by causing a current having the same value as the current flowing in the stray capacitance but having a reverse polarity to flow. The voltage of the housing with respect to the ground of the electric device can be reduced, and even when the housing is not grounded, the human body does not come into contact with the housing and receive an electric shock. In addition, the voltage of the housing with respect to the ground can be reduced with a simple configuration of a transformer and a capacitor or a resistor, an amplifier, and a capacitor, and there is an effect that a compact, lightweight, and low-priced product can be obtained.

The electric shock prevention circuit in the electric equipment of the third and fourth embodiments controls the electric potential of the input of the power converter so that the sum of the voltages of the output of the power converter becomes the same as the electric 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 and receive an electric shock. Even if the load is installed outside the housing and is not connected to the housing, the human body does not come into contact with the case of the load 3 and receive an electric shock. In addition, the voltage of the housing with respect to the ground can be reduced with a simple configuration using a common mode choke coil, a capacitor, a resistor, and an amplifier, and there is an effect that a small size, light weight, and low price can be obtained.

In the electric shock prevention circuit in the electric equipment of the fifth embodiment, the current flowing from the output of the power converter through the stray capacitance to the housing is connected between the ground wire of the input of the power converter and the housing. Since it returns to the power conversion device through the capacitor, the voltage of the housing with respect to the ground can be reduced, and even if the housing is not grounded, the human body does not come into contact with the housing and receive an electric shock. In addition, the voltage of the housing with respect to the ground can be reduced with a simple configuration of the common mode choke coil and the capacitor, and there is an effect that a small size, light weight, and low price can be obtained.

[Brief description of 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 showing an electric shock prevention circuit in an electric device of a second embodiment.

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

FIG. 4 is a circuit diagram showing an electric shock prevention circuit in an electric device of a fourth embodiment.

FIG. 5 is a circuit diagram showing an electric shock prevention circuit in an electric device of a fifth embodiment.

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

FIG. 7 is a waveform chart of each part for explaining the operation of the conventional electric equipment and the embodiment of FIG.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 case 2 power converter 3 load 4 electric equipment 5 AC power supply 6 earth leakage breaker 7 zero-phase current transformer 8 amplifying section 9 trip 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 Lines C1, C2, C3 Capacitor Co Capacitor E Grounding terminals 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)

[Claims] 1. A desired voltage is applied to a load connected to an output of the power conversion device by inputting to the power conversion device an AC power supply having a power conversion device and a load in a housing and one of which is grounded. In an electrical device that outputs a waveform, a capacitor that inverts the voltage between the input ground wire and the output and flows a current equivalent to the current leaking from the stray capacitance of the load or the like is provided between the inverted output and the housing. An electric shock prevention circuit in an electric device, characterized in that the voltage of the casing with respect to the ground is reduced by connecting to the ground. 2. A power converter having a power converter in a housing, and one of the wires of which is grounded is input to the power converter, and a desired voltage waveform is output to a load connected to the output of the power converter. In the electrical equipment, the common mode choke coil is connected between the AC power source and the input of the power converter, and the capacitor is connected between the input lines of the power converter, and the voltage of the output of the power converter is connected. And the voltage difference between the AC power supply ground line and the ground voltage of the AC power source are inverted and amplified, and the potential of the input ground line of the power conversion device is controlled by the inverted amplified output, so that the voltage of the casing with respect to the ground. An electric shock prevention circuit in an electric device, which reduces the electric shock. 3. A desired voltage waveform for a load having an electric power converter and a load in a housing, one of which is grounded and an AC power source is input to the electric power converter, and which is connected to an output of the electric power converter. In an electric device that outputs the above, a common mode choke coil is connected between the AC power supply and the input of the power converter, and a capacitor is connected between the input lines of the power converter, and the power converter is further provided. An electric shock in an electric device characterized in that the voltage of the casing with respect to the ground is reduced by connecting a capacitor having an electrostatic capacity sufficiently larger than the stray capacitance of the load or the like between the input grounding wire and the casing. Prevention circuit.