JP7140700B2 - Electrical equipment with noise filter circuits - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electric device (for example, an air conditioner) equipped with a noise filter circuit that suppresses transmission of high-frequency noise generated by an inverter circuit on a power supply line through which a large current (for example, about 20 [A]) flows.

An electric device including a noise filter circuit is disclosed in Patent Document 1, for example. FIG. 5 is a diagram showing the configuration of the electrical equipment disclosed in Patent Document 1, and in this figure, an air conditioner 200 is exemplified as an electrical equipment provided with a noise filter circuit.

An air conditioner 200 includes an indoor unit 201 having a power relay MRY1 and a terminal plate 2, a terminal plate 3, a noise filter circuit 4, a full-wave rectifier circuit 5, a smoothing capacitor C5, an inverter circuit 6, a compressor 7, and a switching power supply circuit. 8 and an outdoor unit 202 having a microcomputer 9 . The N terminals of the terminal plate 2 and the terminal plate 3 and the L terminals of the terminal plate 2 and the terminal plate 3 are connected by wiring, respectively, and the inverter circuit 6 and the microcomputer 9 are connected via an insulating element (not shown) such as a photocoupler. connected. During operation of the air conditioner 200, a current of about 20 [A] normally flows through the power supply line, and since the capacity of the smoothing capacitor C5 is large, a larger rush occurs when the standby state is shifted to the operating state. Since current flows in the power line, the power relay MRY1 must be designed to withstand such a large current.

During operation of the air conditioner 200, the power relay MRY1 is turned on with the power cord of the indoor unit 201 connected to the external commercial AC power supply 1, and the AC voltage output from the commercial AC power supply 1 is is supplied to the outdoor unit 202 via the indoor unit 201 . The full-wave rectifier circuit 5 and the smoothing capacitor C5 rectify and smooth the supplied AC voltage, and then supply it to the inverter circuit 6 and the switching power supply circuit 8 . The switching power supply circuit 8 generates various DC voltages from the voltage across the smoothing capacitor C5 and supplies them to the microcomputer 9 and other circuits as power supply voltages. The inverter circuit 6 turns on/off an internal power switching element under the control of the microcomputer 9 to convert the voltage across the smoothing capacitor C5 into an AC voltage of a desired frequency. The AC voltage of the desired frequency converted by the inverter circuit 6 is supplied to the compressor 7 to operate the compressor 7 .

In the inverter circuit 6, switching noise is generated by turning on/off the power switching element. This switching noise is transmitted from the power supply line inside the outdoor unit 202 to the indoor unit 201, and finally conducts from the power cord of the indoor unit 201 to the external commercial AC power supply 1, and is connected to the commercial AC power supply 1. equipment. A noise filter circuit 4 is installed in the outdoor unit 202 in order to suppress the conduction of such switching noise.

As shown in FIG. 5, the noise filter circuit 4 includes a discharge resistor R1, a common mode choke coil L1 that suppresses common mode noise, capacitors C1 and C2 that suppress normal mode noise (so-called X capacitors), and a common mode noise suppressor. It has capacitors C3 and C4 (so-called Y capacitors) and a relay RY1. A common mode choke coil L1 and capacitors C1 and C2 are provided between a pair of AC power supply lines LN1 and LN2. Capacitors C3 and C4 are provided between the AC power line LN1 on one side and the main body ground (apparatus main body ground) G of the outdoor unit 202, and the capacitor C4 is provided between the other AC power line LN2 and the outdoor unit 202. and the main body ground G. With these configurations, the noise filter circuit 4 suppresses the conduction of noise to the power supply line of the outdoor unit 202 .

Also, the relay RY1 in the noise filter circuit 4 is provided between the connection node N1 between the capacitors C3 and C4 and the main body ground G of the outdoor unit 202 . Each end of the relay coil of relay RY1 is connected to the output side of switching power supply circuit 8 .

When the air conditioner 200 shown in FIG. 5 is in a standby state, that is, when the power relay MRY1 is off, there is no power supply from the commercial AC power supply 1 to the outdoor unit 202, so the switching power supply circuit 8 does not operate. , no voltage is applied across the relay coil of relay RY1. Therefore, in air conditioner 200 in the standby state, relay RY1 is turned off. Moreover, the noise filter circuit 4 stops functioning as a noise filter because the relay RY1 is turned off.

Therefore, when the air conditioner 200 is in the standby state, the connection node N1 and the main body ground G are cut off, and no leakage current flows. In the standby state, the inverter circuit 6 does not operate and no switching noise is generated. Therefore, no problem occurs even if the noise filter circuit 4 does not function as a noise filter.

On the other hand, in the operating state, that is, when the power relay MRY1 is ON, power is supplied from the commercial AC power supply 1 to the outdoor unit 202, and the switching power supply circuit 8 operates. When the switching power supply circuit 8 operates, a predetermined voltage (Vcc-0 [V], such as 12 [V], 24 [V], etc.) is applied across the relay coil of the relay RY1, turning on the relay RY1. When the relay RY1 is turned on, the noise filter circuit 4 functions as a noise filter and can suppress conduction of switching noise generated in the inverter circuit 6. FIG. Also, in the operating state, a leakage current flows from the connection node N1 to the main body ground G, but the leakage current level at this time is low.

As described above, the noise filter circuit 4 shown in FIG. 5 includes a relay RY1 that is turned on/off under the control of the switching power supply circuit 8. In the standby state, the relay RY1 is turned off to suppress leakage current, and in the operating state, the relay RY1 is turned off. The switching noise can be suppressed by turning on the relay RY1. Further, since only a leakage current flows through the relay RY1 in the operating state, a low-current type relay, that is, a low-cost and small-sized relay can be used as the relay RY1.

Japanese Patent No. 5031444

The electric device disclosed in Patent Document 1 (here, the air conditioner 200) can suppress both high-frequency noise and leakage current without significantly increasing the cost or size of the components mounted in the noise filter circuit 4. It's the best you can do.

However, even in such an electrical device, if it is equipped with a surge protection circuit that protects the electrical device from surge currents such as lightning, a high voltage will be applied between the contacts of relay RY1 in the withstand voltage test, resulting in NG ( The inventors of the present application have discovered that there is a case where the product is determined to be defective. This is explained below.

An air conditioner 200' shown in FIG. 6 has a configuration in which a surge absorber SA1 and a varistor NR1 are added as a surge protection circuit to the air conditioner 200 shown in FIG. Surge absorber SA1 and varistor NR1 are connected in series between AC power supply line LN2 and main body ground G. FIG.

FIG. 7 is a circuit diagram in which only the parts related to the withstand voltage test are extracted from the air conditioner 200'. In the dielectric strength test, since a test voltage is applied between the power supply section and the ground section by the dielectric strength test power supply 10, the equivalent circuit for the dielectric strength test is as shown in FIG. As shown in FIG. 8, during the withstand voltage test, the commercial AC power supply 1 is not connected, and the AC power supply lines LN1 and LN2 are directly connected to each other.

Also, in FIG. 7, a resistor R2, not shown in FIGS. 5 and 6, is connected in parallel with the relay RY1. This resistor R2 has the function of reducing the voltage between the contacts of the relay RY1. The lower the resistance value of the resistor R2, the higher the effect of lowering the voltage between the contacts of the relay RY1. However, in the circuit shown in FIG. 7, the presence of the resistor R2 causes leakage current in the standby state, and if the resistance value of the resistor R2 is low, the leakage current also increases. I don't like doing it.

In the withstand voltage test, an AC voltage of 1.8 kV (with a frequency of 50 Hz or 60 Hz) is normally applied for 1 second (for 200 V models). Here, the voltage (voltage between contacts) applied to the relay RY1 is 1.8 kV without the resistor R2, but is 1800×r2/(r2+z1) [V] with the resistor R2. Here, r2 is the resistance value [Ω] of resistor R2, and z1 is the impedance [Ω] of capacitors C3 and C4. Also, the impedance z1 of the capacitors C3 and C4 is expressed by z1=1/(2Π·f·(c3+c4)). Here, f is the frequency [Hz] of the test voltage, and c3 and c4 are the capacitance values [F] of the capacitors C3 and C4, respectively.

Capacitors C3 and C4, which are Y capacitors, are generally F-characteristic capacitors whose capacitance varies with temperature, and the F-characteristic capacitor reaches its maximum capacitance in an environment of 10.degree. Therefore, the voltage between the contacts of relay RY1 becomes the highest under the 10° C. environment.

In the relay RY1, when the voltage across the contacts exceeds the breakdown voltage, the relay RY1 causes chattering, and the voltage across the contacts further increases. The increase in the voltage across the terminals of the relay RY1 due to chattering can be explained by the equivalent circuit shown in FIG. Here, L represents the inductance component of the power line, the ferrite core attached to the power line, and the pattern. When the relay RY1 repeats ON/OFF due to chattering, energy is generated in the inductance component L, and this energy increases the voltage across the terminals of the relay RY1.

When the voltage across the terminals of relay RY1, which has risen due to chattering, becomes higher than the discharge voltage of the surge protection circuit (surge absorber SA1 or varistor NR1), the surge protection circuit may conduct, resulting in NG in the withstand voltage test. . That is, in the air conditioner 200' shown in FIG. 6, there is a problem that NG is likely to occur in the withstand voltage test during production in winter when the air temperature drops and the capacities of the capacitors C3 and C4 increase. This problem can be solved by lowering the resistance value of the resistor R2, but in that case, there arises a problem of increased leakage current during the standby state.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrical device equipped with a noise filter circuit that can withstand a dielectric strength test while suppressing an increase in leakage current in a standby state. do.

In order to solve the above-described problems, a first aspect of the present invention provides an inverter circuit and a high-frequency power supply of the inverter circuit on a pair of power supply lines for supplying a voltage based on an output voltage of an external power supply to the inverter circuit. and a noise filter circuit for suppressing noise conduction, wherein the noise filter circuit has a first capacitor, a second capacitor, a switching relay, and a positive temperature coefficient thermistor, and the first capacitor and the second capacitor is provided between the other power line and the equipment main body ground, and the switching relay and the positive temperature coefficient thermistor are connected to the first capacitor and the connection node between the second capacitor and the equipment main body ground are connected in parallel with each other.

According to the above configuration, in winter when the temperature drops, the capacitance values of the first and second capacitors of the F characteristic increase, and the voltage between the contacts of the switching relay increases. value decreases. As a result, even in winter when the temperature drops and the capacities of the first and second capacitors increase, NG in the dielectric strength test can be suppressed. Also, when the air temperature is not low, the resistance value of the PTC thermistor becomes high, so that the leakage current during the standby state can be suppressed.

Further, in the electric device, the noise filter circuit further has a resistor, the resistor is connected in series with the PTC thermistor, and the PTC thermistor and the resistor are connected in parallel with a switching relay. It can be configured as

According to the above configuration, by connecting a resistor in series with the PTC thermistor, it is possible to prevent the resistance of the path through which the leakage current flows during the standby state from dropping too much, and increase the leakage current when the temperature drops. can be suppressed.

Further, in the above electric device, the switching relay may have a configuration in which two relays are connected in series.

According to the above configuration, the voltage between the contacts of each relay can be halved compared to the case where one relay is used as the switching relay. As a result, chattering in each relay is less likely to occur in the dielectric strength test, and NG in the dielectric strength test can be suppressed.

In order to solve the above problems, a second aspect of the present invention provides an inverter circuit, and a pair of power supply lines for supplying a voltage based on an output voltage of an external power supply to the inverter circuit. and a noise filter circuit for suppressing transmission of high-frequency noise, wherein the noise filter circuit has a first capacitor, a second capacitor, and a switching relay, and the first capacitor is connected to one power supply The second capacitor is provided between the other power supply line and the equipment body ground, and the switching relay connects the first capacitor and the second capacitor. It is characterized in that the switching relay has a configuration in which two relays are connected in series.

In the electrical equipment provided with the noise filter circuit of the present invention, the resistance value of the PTC thermistor decreases at the same time in winter when the capacities of the first and second capacitors increase, thereby suppressing NG in the withstand voltage test. Otherwise, the positive temperature coefficient thermistor has a high resistance value, which has the effect of suppressing the leakage current during the standby state.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the configuration of an electrical device shown in Embodiment 1, and is a diagram showing the configuration of an air conditioner exemplified as the electrical device; FIG. 2 is a circuit diagram in which only a part related to a withstand voltage test is extracted from the air conditioner shown in Embodiment 1; FIG. 11 is a circuit diagram showing only a portion related to a withstand voltage test extracted from the air conditioner shown in Embodiment 2; FIG. 10 is a circuit diagram showing only a portion related to a withstand voltage test extracted from the air conditioner shown in Embodiment 3; FIG. 1 is a diagram showing a general configuration of an air conditioner as an electric device having a conventional noise filter circuit. FIG. 6 is a diagram showing a configuration in which a surge protection circuit is added to the air conditioner of FIG. 5; FIG. 7 is a circuit diagram in which only a portion related to a withstand voltage test is extracted from the air conditioner shown in FIG. 6; FIG. 7 is an equivalent circuit diagram at the time of a withstand voltage test in the air conditioner shown in FIG. 6; 7 is an equivalent circuit diagram for explaining an increase in voltage between relay terminals due to chattering in the air conditioner shown in FIG. 6. FIG.

[Embodiment 1]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing the configuration of the electrical equipment shown in Embodiment 1. In this figure, an air conditioner 100 comprising an indoor unit 101 and an outdoor unit 102 is exemplified as an electrical equipment equipped with a noise filter circuit. ing. The air conditioner 100 shown in FIG. 1 is the air conditioner 200' shown in FIG. It has the same configuration as the machine 200'. 1 that are the same as those in FIG. 6 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The thermistor PTC1 is connected in parallel with the relay RY1. FIG. 2 is a circuit diagram in which only the parts related to the withstand voltage test are extracted from the air conditioner 100 shown in FIG. In the circuit shown in FIG. 2, the resistor R2 in the circuit shown in FIG. 7 is replaced with a thermistor PTC1. Further, in the air conditioner 100, the capacitor C3 and the capacitor C4 correspond to the first capacitor and the second capacitor recited in the claims, the relay RY1 corresponds to the switching relay recited in the claims, and the AC Power supply lines LN1 and LN2 correspond to a pair of power supply lines.

When performing a withstand voltage test on the air conditioner 100 according to Embodiment 1, the voltage between the contacts of the relay RY1 is 1800×r _PTC /(r _PTC +z1) [V] due to the presence of the thermistor PTC1. Here, r _PTC is the resistance value [Ω] of the thermistor PTC1. Also, the impedance z1 of the capacitors C3 and C4 is z1=1/(2Π·f·(c3+c4)).

As described above, the capacitance values c3 and c4 of the F-characteristic capacitors C3 and C4 increase in winter when the temperature drops, and the impedance z1 also increases at this time. An increase in impedance z1 acts to increase the voltage across the contacts of relay RY1. On the other hand, the thermistor PTC1 decreases in resistance as the temperature decreases, and acts to decrease the voltage between the contacts of the relay RY1. That is, when the air temperature decreases and the impedance z1 increases, the resistance value of the thermistor PTC1 decreases at the same time. Since the voltage between the contacts of the relay RY1 is reduced by reducing the resistance value of the thermistor PTC1, the air conditioner 100 suppresses NG in the withstand voltage test even in winter when the capacities of the capacitors C3 and C4 increase. be able to.

Further, when the temperature is not low, the resistance value of the thermistor PTC1 is maintained at a high resistance, so that leakage current flowing through the thermistor PTC1 in the standby state can be suppressed.

[Embodiment 2]
FIG. 3 is a circuit diagram in which only the parts related to the withstand voltage test are extracted from the air conditioner 100 according to the second embodiment. The circuit shown in FIG. 3 is obtained by adding a resistor R3 to the circuit shown in FIG. Resistor R3 is connected in series with thermistor PTC1, and thermistor PTC1 and resistor R3 are connected in parallel with relay RY1. Note that the air conditioner 100 according to Embodiment 2 has the same configuration as the air conditioner 100 according to Embodiment 1, except that a resistor R3 is added.

The air conditioner 100 according to Embodiment 1 has a configuration in which only the thermistor PTC1 is connected in parallel with the relay RY1. To increase. On the other hand, in the air conditioner 100 according to Embodiment 2, by connecting the resistor R3 in series with the thermistor PTC1, the resistance of the path through which the leakage current flows during the standby state is prevented from decreasing too much. It is possible to suppress an increase in leakage current when the temperature drops.

[Embodiment 3]
FIG. 4 is a circuit diagram extracting and describing only the part related to the withstand voltage test from the air conditioner 100 according to the third embodiment. The circuit shown in FIG. 4 is configured by removing the thermistor PTC1 from the circuit shown in FIG. 2 and instead connecting two relays RY1 and RY2 in series. The air conditioner 100 according to Embodiment 3 has the same configuration as the air conditioner 100 according to Embodiment 1 except that the thermistor PTC1 is eliminated and two relays RY1 and RY2 are connected in series. do.

In the air conditioner 100 according to Embodiment 3, the two relays RY1 and RY2 are connected in series, so that the voltage between the contacts of each relay is halved compared to the case where one relay RY1 is used. can be made As a result, chattering in each relay is less likely to occur in the dielectric strength test, and NG in the dielectric strength test can be suppressed.

In the air conditioner 100 according to Embodiment 3, the chattering of the relay in the withstand voltage test can be prevented without using the thermistor PTC1 and the resistor R3 shown in FIGS. 2 and 3 or the resistor R2 shown in FIG. can be suppressed, and NG in the withstand voltage test can be suppressed. However, the present invention is not limited to this, and thermistor PTC1, resistor R3, or resistor R2 may be connected in parallel with the two relays RY1 and RY2.

The embodiments disclosed this time are exemplifications in all respects and are not grounds for restrictive interpretation. Therefore, the technical scope of the present invention is not to be interpreted only by the above-described embodiments, but is defined based on the claims. In addition, all changes within the meaning and range of equivalents to the scope of claims are included.

1 Commercial AC Power Supply 2, 3 Terminal Board 4 Noise Filter Circuit 5 Full Wave Rectifier Circuit 6 Inverter Circuit 7 Compressor 8 Switching Power Supply Circuit 9 Microcomputer 100 Air Conditioner (Electrical Equipment)
101 indoor unit 102 outdoor unit LN1, LN2 AC power lines (pair of power lines)
C1, C2 capacitor C3 capacitor (first capacitor)
C4 capacitor (second capacitor)
C5 Smoothing capacitor L1 Common mode choke coil MRY1 Power relay PTC1 Positive characteristic thermistor R3 Resistor RY1, RY2 Relay (switching relay)
SA1 Surge absorber NR1 Varistor G Body ground (Equipment body ground)

Claims (3)

An electrical device comprising an inverter circuit and a noise filter circuit for suppressing transmission of high-frequency noise of the inverter circuit on a pair of power supply lines for supplying the inverter circuit with a voltage based on the output voltage of an external power supply ,
The noise filter circuit has a first capacitor, a second capacitor, a switching relay and a positive temperature coefficient thermistor,
the first capacitor is provided between one of the pair of power supply lines and the equipment main body ground;
the second capacitor is provided between the other of the pair of power supply lines and the equipment main body ground;
The switching relay and the positive temperature coefficient thermistor are connected in parallel between a connection node between the first capacitor and the second capacitor and the equipment main body ground. electrical equipment. The electrical device according to claim 1,
The noise filter circuit further has a resistor,
An electrical device, wherein the resistor is connected in series with the positive temperature coefficient thermistor, and the positive temperature coefficient thermistor and the resistor are connected in parallel with a switching relay. The electrical device according to claim 1 or 2,
The electric device, wherein the switching relay has a configuration in which two relays are connected in series.

Images