JP2003204674A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain cost reduction by miniaturizing a power converter. <P>SOLUTION: A diode D2 of a diode snubber circuit 6 rectifies spike voltage, a capacitor C7 accumulates the rectified voltage, and a resistor R1 consumes current accumulated in the capacitor C7. The diode snubber circuit 6, having an operation thus performed, supplies power accumulated in the capacitor C7 to an amplifying part 5. Thus by supplying the power to the amplifying part 5 from the diode snubber circuit 6 for suppressing the voltage applied to a switching element Q1, the need for a constant voltage circuit for supplying power to the amplifying part 5 is eliminated, and low breakdown voltage transistors can be used for transistor Q11, Q12 of the amplifying part 5, so as to reduce the cost. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a power converter.

[0002]

2. Description of the Related Art A power converter is generally provided with a line filter on the power supply side for reducing noise.

However, when the capacity of the power conversion device becomes large and the power conversion device is used for large power, the line filter becomes large. Therefore, a power conversion device equipped with an active noise reduction circuit has been proposed.

The configuration of such a power converter is shown in FIG.
The power conversion device 50 includes a rectifying / smoothing unit 51 and a power conversion unit 5.
2, a leakage current detection unit 53, an amplification unit 54, and a constant voltage circuit unit 55.

The rectifying / smoothing section 51 rectifies and smoothes the AC voltage supplied from the AC power source 56 to generate a DC voltage. The power conversion unit 52 converts the DC power generated by the rectifying / smoothing unit 51 into DC power supplied to the load R50.

The leak current detector 53 detects leak current superimposed on the power supply line from the AC power supply 56. The amplification unit 54 amplifies the detection signal of the leakage current detected by the leakage current detection unit 53 and supplies a compensation current to the ground line in a direction of canceling the leakage current.

The constant voltage circuit section 55 rectifies and smoothes the AC voltage from the AC power supply 56, and supplies a constant DC voltage to the amplifier section 54 for amplifying the leak current detection signal of the amplifier section 54. .

In the power converter 50, the AC power source 5
The leakage current detector 53 detects the leakage current superimposed on the power supply line from 6. The amplification unit 54 includes a leakage current detection unit 53.
Amplifies the detection signal of the leakage current detected by, and supplies the amplified current as a compensation current to the ground line in the direction of canceling the leakage current. The active noise reduction circuit is composed of the leakage current detection unit 53 and the amplification unit 54, and the power conversion device 50 thus cancels the leakage current with the compensation current to reduce noise.

[0009]

However, since the leakage current detecting section 53 and the amplifying section 54 operate in this manner, the power conversion device requires a constant voltage source for supplying power to the amplifying section 54. Is coming. In the conventional power converter, the constant voltage circuit unit 55 is provided closer to the AC power supply 56 than the power converter 52. Therefore, the voltage in the amplifier 54 becomes high,
A semiconductor having a high breakdown voltage is required for the semiconductor forming the amplifying section 54, which causes a cost increase.

Further, since the constant voltage circuit section 55 is provided, the constant voltage circuit section 55 impedes downsizing of the power conversion device 50.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a power conversion device which can be downsized.

[0012]

In order to achieve this object, a power converter according to a first aspect of the present invention is a power converter for converting power via a transformer and a ground line from the power converter. A leakage current detection unit that detects a leakage current flowing through the power supply line via the, and amplifies the detection signal of the leakage current detected by the leakage current detection unit, the amplified current in the direction of canceling the leakage current. And a snubber unit that reduces a spike voltage generated in the transformer of the power conversion unit, the snubber unit rectifying and smoothing the reduced spike voltage to generate the spike voltage. The generated DC power is supplied to the amplification unit as a current supply source that amplifies the detection signal.

With such a structure, it is possible to reduce the size.

The amplifying section may include a Zener diode for limiting the voltage level of the DC voltage supplied from the snubber section.

The snubber section has a diode whose anode is connected to one terminal of a primary winding of the transformer and rectifies a spike voltage generated in the primary winding of the transformer, and a primary of the transformer. It may be configured by a diode snubber circuit including a capacitor connected between the other terminal of the side winding and the cathode of the diode, and a resistor connected in parallel with the capacitor.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A power converter according to an embodiment of the present invention will be described below with reference to the drawings. The configuration of the power conversion device according to this embodiment is shown in FIG. The power conversion device includes a noise filter unit 1, a rectifying / smoothing circuit unit 2, a power conversion circuit unit 3, a leakage current detection unit 4, an amplification unit 5, and a diode snubber circuit 6. .

The noise filter section 1 includes capacitors C1 and C1.
It is provided with C2, C3, C4 and a choke coil L1. The capacitors C1 and C2 are across-the-line capacitors that attenuate normal mode noise, and are connected between a pair of power supply lines of the AC power supply 7. The capacitors C3 and C4 are capacitors for reducing common mode noise, and are connected between each of the pair of power supply lines and the ground line.

The choke coil L1 is a common mode choke coil that attenuates common mode noise, and is connected in series to each of a pair of power supply lines of the AC power supply 7 with the same winding direction.

The rectifying / smoothing circuit section 2 comprises a rectifying circuit 11 and a capacitor C5. The rectifier circuit 11 rectifies the AC voltage supplied from the AC power supply 7, and is connected to a pair of power supply lines. The rectifier circuit 11 is composed of, for example, a bridge rectifier circuit including four diodes.

The capacitor C5 is a capacitor for smoothing the pulsating flow of the rectified voltage output from the rectifier circuit 11, and is connected to the output end of the rectifier circuit 11.

The power conversion circuit unit 3 converts a predetermined DC power into a DC power having a predetermined voltage and supplies the DC voltage to the load R0. The transformer T and the switching element Q are provided.
1, a diode D1, and a capacitor C6,
It constitutes a flyback converter.

The transformer T is for transmitting electric power on the primary side to the secondary side, and has a primary winding n1 and a secondary winding n2.
It has and. The primary winding n1 is a winding for generating a voltage by a switching current to generate excitation energy in the transformer T, and the secondary winding n2 is a primary winding n1.
1 is a winding for generating a voltage by the excitation energy generated in 1. One end Pt11 of the primary winding n1 is connected to the positive (+) terminal of the capacitor C5. Secondary winding n
2 has a primary winding n so that it has a polarity opposite to that of the primary winding n1.
It is wound in the opposite direction to 1.

The switching element Q1 is an element for supplying a signal S1 to switch the current flowing through the primary winding n1 of the transformer T to induce a voltage in the primary winding n1 of the transformer T. It is connected between the other end Pt12 of the primary winding n1 of T and the negative (-) terminal of the capacitor C5. A control unit (not shown) supplies a pulsed signal S1 to the switching element Q1 and performs PWM control based on fixed oscillation to stabilize the output voltage.

The diode D1 is a switching element Q1.
Is a diode for blocking the flow of current during the on period when is turned on and for rectifying the current from the voltage generated in the secondary winding n2 during the off period.

The capacitor C6 is for smoothing the current passing through the diode D1 to generate a DC voltage in the off period, and has a cathode of the diode D1 and an output terminal (+) and an output terminal (-). , Connected between. The power conversion circuit unit 3 supplies the generated DC voltage to the load R0.

The diode snubber circuit 6 includes a capacitor C
7, a resistor R1 and a diode D2. The anode of the diode D2 is connected to the terminal Pt12 of the transformer T. Both the capacitor C7 and the resistor R1
It is connected between the terminal Pt11 of the transformer T and the cathode of the diode D2.

The leakage current detector 4 detects the leakage current, and is a primary winding in which the electric wires of the lines E1 and E2 are wound around the magnetic core of a through-type zero-phase current transformer (not shown). And a secondary winding for extracting an induced current as a detection signal. The line E1 is a line connecting the positive electrode of the capacitor C5 of the rectifying and smoothing circuit unit 2 and the negative electrode of the capacitor C7 of the diode snubber circuit 6, and the line E2 is the negative electrode of the capacitor C5 and the current downstream side of the switching element Q1. It is a line that connects the terminal. The turn ratio between the primary winding and the secondary winding is set to 1.

The amplification section 5 amplifies the induced current generated in the secondary winding of the leakage current detection section 4 and supplies the amplified current as a compensation current to the ground line in the direction of canceling the leakage current. Yes, it includes transistors Q11 and Q12 and a capacitor C8.

The transistor Q11 is an NPN type bipolar transistor, and its collector is connected to the positive side (+) of the capacitor C7. Transistor Q
Reference numeral 12 is a PNP-type bipolar transistor, the emitter of which is connected to the emitter of the transistor Q11 and the collector of which is connected to the negative electrode (−) of the capacitor C7.

The one end of the secondary winding of the leakage current detector 4 has a base of the transistor Q11 and a transistor Q1.
2 is connected to the base and the other end is connected to the transistor Q11.
Of the transistor Q12 and the emitter of the transistor Q12. The amplification factors of the transistors Q11 and Q12 are sufficiently larger than 1, and the amplification factor of the amplification section 5 is 1.

The capacitor C8 is a capacitor for supplying a compensating current to the ground line, and is the transistor Q1.
1, Q12 is connected between the base and the ground line.

Next, the operation of the power conversion device according to this embodiment will be described. As shown in FIG.
A signal S1 as shown in is supplied. When the signal S1 goes high, the switching element Q1 turns on and the signal S1
When 1 becomes low level, the switching element Q1 is turned off. Times t0 to t1 are an on period in which the switching element Q1 is on, and times t1 to t2 are an off period in which the switching element Q1 is off.

When the switching element Q1 is turned on and off, the current flowing in the primary winding n1 of the transformer T is switched, and a voltage is generated in the primary winding n1 of the transformer T.

During the ON period, on the primary side of the transformer T, as shown in FIG.
The voltage Vq1 applied to the switch becomes substantially zero, and the current Iq1 shown in FIG. 2C flows through the switching element Q1.

On the secondary side of the transformer T, since the secondary winding n2 of the transformer T has the opposite polarity to the primary winding n1, the diode D1 prevents the current from flowing and
The next winding n2 is in an open state. Excitation energy is accumulated in the transformer T during this ON period. A voltage Vt1 as shown in FIG. 2D is applied to the primary winding n1 of the transformer T.

In the off period, the voltage Vq1 applied to the switching element Q1 becomes higher than the charging voltage of the capacitor C5 as shown in FIG. 2 (b), and the current Iq1 flowing through the switching element Q1 becomes It becomes zero as shown in c).

On the secondary side of the transformer T, the diode D1 conducts, the transformer T releases the accumulated excitation energy, and based on this excitation energy, the secondary winding n2 passes through the diode D1 and a capacitor. A current I2 as shown in FIG. 2 (e) flows through C6. The current I2 flows out at a ratio inversely proportional to the turn ratio between the primary winding n1 and the secondary winding n2 of the transformer T based on the maximum current value of the current Iq1, and decreases while releasing the exciting energy, and the transformer T
The current value becomes 0 at the time when all the accumulated excitation energy is discharged.

In the off period, the inductance of the transformer T and the inductance of the wiring cause
A spike voltage is generated in the voltage Vq1 as shown in FIG. 2B and the voltage Vt1 as shown in FIG. The diode snubber circuit 6 lowers the voltage level of this spike voltage. This operation will be described later.

The capacitor C6 smoothes the current rectified by the diode D1. As a result, a DC voltage is generated, and the power conversion circuit unit 3 supplies the generated DC voltage to the load R0.

When the switching element Q1 switches, a leakage current Is as shown in FIG. 2 (f) flows through the ground line via the capacitors C3 and C4 between the ground in the circuit of the power converter. This is a factor in the generation of common mode noise.

When the primary current (currents of the lines E1 and E2) flows through the primary winding of the leakage current detector 4, an induced current flows through the secondary winding. Since the turn ratio between the primary winding and the secondary winding of the leakage current detector 4 is 1, the current value of the induced current flowing through the secondary winding becomes the same as the current value of the primary current.

In the positive half cycle, this induced current is shunted to flow into the base of transistor Q11 as a base current. Due to the flow of the induced current, the potential of the emitter of the transistor Q11 rises. Further, the induced current flows to the base of the transistor Q11, so that the potential of the base of the transistor Q11 also rises. Since the amplification factor of the transistor Q11 is sufficiently larger than 1 and the amplification factor of the amplification unit 5 becomes 1, a current having the same current value as the leakage current Is is generated.

In the negative half cycle, the circuit of the transistor Q12 operates similarly to the circuit of the transistor Q11, and a current having the same current value as the leakage current Is is generated. This transistor Q11 circuit and transistor Q
By combining with the circuit of 12, the compensation current Ir as shown in FIG. 2 (g) is generated.

Then, the compensation current Ir is changed to the leakage current Is.
By supplying the ground line through the capacitor C8 in the opposite direction to the above, the leakage current Is becomes small as shown in FIG. 2 (h). Thereby, common mode noise can be reduced.

Next, the operation of the diode snubber circuit 6 will be described. The diode D2 rectifies the spike voltage generated by the inductance of the transformer T and the wiring, the capacitor C7 stores the rectified voltage, and the resistor R1 consumes the current stored in the capacitor C7. The diode snubber circuit 6 having such an action is composed of the capacitor C.
The power stored in 7 is supplied to the amplification unit 5.

Without the diode snubber circuit 6, the spike voltage of the primary voltage Vt1 of the transformer T (or the voltage Vq1 of the switching element Q1) becomes high as shown by the broken line in FIG. However, as the diode snubber circuit 6 operates in this way, the spike voltage decreases as shown by the solid line. Since the spike voltage is reduced in this way, the voltage applied to the switching element Q1 is suppressed.

The diode snubber circuit 6 includes a capacitor C.
The power stored in 7 is supplied to the amplification unit 5. Transformer T
The generated electric power changes due to the current flowing through the inductance, and the maximum output electric power and the maximum electric power consumed by the diode snubber circuit 6 are obtained. The resistance value of the resistor R1 that consumes this power is normally set so that the output voltage is constant.

Therefore, the spike voltage generated in the primary winding n1 of the transformer T is almost equal to the primary winding n of the transformer T.
It is determined by the turn ratio of the primary winding and the secondary winding n2 and the output voltage,
If the output voltage is constant, this spike voltage is also constant. In addition, since the ON / OFF ratio of the switching element Q1 is usually set to be 1: 1 when the supply voltage is the lowest, even when the ON period is extended, this spike voltage is a power supply voltage (for example, , 100 V).

Therefore, if the voltage based on this spike voltage is supplied from the diode snubber circuit 6 to the amplifier 5,
It is not necessary to provide a constant voltage circuit unit for supplying power to the amplification unit 5, and the voltage supplied to the amplification unit 5 is low, so that a substantially constant voltage can be supplied to the amplification unit 5. That is,
The breakdown voltage of the transistors Q11 and Q12 can be kept low.

As described above, according to the present embodiment, originally, the power is supplied from the diode snubber circuit 6 included in the power converter to the amplifying section 5 in order to suppress the voltage applied to the switching element Q1. I decided to do it.
Therefore, a constant voltage circuit for supplying electric power to the amplifying unit 5 is not required, the size can be reduced, and the transistor Q1 of the amplifying unit 5
Since a low withstand voltage can be used for 1 and Q12, the cost can be reduced. Further, since the electric power to be consumed by the resistor R1 can be used, the electric power can be supplied to the amplifying unit 5 without lowering the efficiency of the entire power conversion device.

Various modes are conceivable for carrying out the present invention, and the present invention is not limited to the above-described modes. For example, as shown in FIG. 4, Zener diodes D11 and D12 and capacitors C11 and C1 are provided in the amplification unit 5.
By including 2 and the resistors R11 and R12, the voltage limiting characteristic can be added.

That is, the anode of the Zener diode D11 is connected to one end of the resistor R11, the cathode of the Zener diode D11 is connected to the collector of the transistor Q11, and the other end of the resistor R11 is connected to the transistor Q11.
Connected to the base of. Also, the capacitor C11
Is connected between the base of the transistor Q11 and the leakage current detector 4.

The cathode of the Zener diode D12 is connected to one end of the resistor R12, the anode of the Zener diode D12 is connected to the collector of the transistor Q12, and one end of the resistor R12 is connected to the transistor Q12.
Connected to the base of. Also, the capacitor C12
Are connected between the base of the transistor Q12 and the leakage current detector 4.

With such a configuration, the amplification section 5 has the voltage limiting characteristic as shown in FIG. In the diode snubber circuit 6 shown in FIG. 1, since the primary side voltage of the transformer T is constant and the resistance value of the resistor R1 is constant, the same electric power is consumed even under a light load as during a heavy load. However, since the amplification unit 5 has the characteristics shown in FIG. 5, the power consumption of the amplification unit 5 is reduced and the efficiency is improved when the load is light.

Further, as shown in FIG. 6, the diode snubber circuit 6 may be provided with a Zener diode D21.

The configuration of the amplifying section 5 is not limited to the above-described configuration, and PNP type bipolar transistors can be used for the transistors Q11 and Q12, and N type FET (field effect transistor) and P type FET are used.
Can also be used. In addition, the amplifier 5 has two NPs.
An N-type bipolar transistor may be provided, and two secondary windings of the leakage current detector 4 may be provided to supply current to each of the two transistors.

[0057]

As described above, according to the present invention,
The power converter can be downsized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a power conversion device according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing an operation of the power conversion device of FIG.

FIG. 3 is an explanatory diagram in which a voltage waveform supplied to a transformer is enlarged.

FIG. 4 is a circuit diagram showing another configuration of the amplification section of FIG.

5 is an explanatory diagram showing the operation of the amplification section of FIG. 4. FIG.

FIG. 6 is a circuit diagram showing another configuration of the snubber circuit of FIG.

FIG. 7 is a block diagram showing a configuration of a conventional power conversion device.

[Explanation of symbols]

1 Noise filter section 3 Power conversion circuit section 4 Leakage current detector 5 Amplifier 6 diode snubber circuit

Claims (3)

[Claims] 1. A power converter for converting power via a transformer, a leak current detector for detecting leak current flowing from the power converter to a power supply line via a ground line, and the leak current detector. A snubber that amplifies the detection signal of the detected leakage current and reduces the spike voltage generated in the amplification unit that supplies the amplified current to the ground line in a direction that cancels the leakage current and the transformer of the power conversion unit. The snubber unit rectifies and smoothes the reduced spike voltage, and supplies the generated DC power to the amplification unit as a current supply source that amplifies the detection signal. There is a power converter. 2. The power conversion device according to claim 1, wherein the amplification unit includes a Zener diode that limits the voltage level of the DC voltage supplied from the snubber unit. 3. The snubber portion includes a diode whose anode is connected to one terminal of a primary winding of the transformer and rectifies a spike voltage generated in the primary winding of the transformer, and a diode of the transformer. A capacitor connected between the other terminal of the primary winding and the cathode of the diode, and a resistor connected in parallel with the capacitor, and a diode snubber circuit comprising: The power conversion device according to claim 1 or 2, characterized in that.