JP3044650B2 - Power converter noise reduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device in a power converter including a switching element such as an inverter device.

[0002]

2. Description of the Related Art A conventional inverter shown in FIG. 1 has a rectifier circuit 3 connected to an AC power supply 1 via a line filter 2, and a smoothing device connected between a pair of output terminals of the rectifier circuit 3. It comprises a capacitor 4 and an inverter circuit 5 connected to the smoothing capacitor 4. The line filter 2 includes reactors L connected in series to three power lines between the three-phase AC power supply 1 and the rectifier circuit 3, respectively, and removes high-frequency noise components. The inverter circuit 5 is an IGBT
It includes a switching element Q such as an insulated gate bipolar transistor, and generates an output voltage V0 which is pulse width modulated (PWM) by turning on and off. In FIG. 1, a three-phase induction motor 6 is connected as a load of the inverter circuit 5.

[0003]

Since the output voltage V0 of the inverter circuit 5 is a pulse voltage, it leaks into the capacitance between each winding of the induction motor 6 and the ground, that is, the straight capacitance C. When the current Ic is C.dv / dt
Flows in When the switching element Q is a third-generation IGBT, dv / dt is about 3000 v / μs, and a pulse current of about 3 A flows when the capacitance is 1000 pF. The pulse current flows as a high-frequency common mode noise through a circuit including the AC power supply 1, the induction motor 6, and the ground. Although the line filter 2 has a function of removing noise, a sufficient noise removing effect cannot be obtained as the on / off frequency of the switching element Q increases. Although the power supply 1 shown in FIG. 1 is of a three-phase type, a common-mode noise also occurs in the case of a single-phase power supply. Also, when the middle point of the three-phase induction motor 6 is grounded, a leakage current, that is, a zero-phase current flows as common mode noise. The common mode noise as described above causes an electric shock and a ground fault breaker operation. In a power converter including a switching element, a normal mode which circulates through a circuit from the power supply 1 to the electric motor 6 as a load also poses a problem. Noise can be removed to some extent by a reactor or a filter composed of a combination of a reactor and a capacitor. However, in order to enhance the noise removal effect, it is necessary to use a large reactor, and the noise filter becomes large and expensive.

Accordingly, an object of the present invention is to reduce the size, cost, and performance of a noise reduction device for a power conversion device.

[0005]

According to the first aspect of the present invention, there is provided a rectifier circuit connected to an AC power supply.
And a rectifier circuit connected between a pair of DC output terminals of the rectifier circuit.
Connected to the smoothing capacitor.
Inverter was - made up of a capacitor circuit, said inverter - a noise reduction device in a power conversion apparatus for converting power on the basis of the on and off of <br/> switching element capacitor circuit, wherein
The leakage current flowing from the load of the inverter circuit to the ground
The AC power supply and the regulator for detecting as a noise current.
And connected leak current detection means between the flow circuit, said motor
Re wherein in response to the detected leakage current by the current detecting means motor
Re forms a compensation current of the current in the opposite direction, and a compensation current supply circuit for supplying the compensation current to the line flowing of leakage current of the power converter, the compensation current supply circuit
Is connected between one end of the smoothing capacitor and ground.
Of the connected first current control element and the smoothing capacitor.
Second current control element connected between the other end and ground
And at least one of the first and second electrodes.
The current control element responds to the current detected by the leakage current detection means.
The present invention relates to a noise reduction device, which supplies the compensation current in response . Also, billing
Item 2 is a rectifier circuit connected to an AC power supply,
A smoothing capacitor connected between a pair of DC output terminals of the rectifier circuit
Capacitor and the inverter connected to the smoothing capacitor.
Power between the AC circuit and the rectifier circuit.
For first and second line filters connected between lines
And a line filter including a series circuit of capacitors.
The switching element of the inverter circuit is turned on or off.
Noise in power converters that convert power based on
Noise reduction device, wherein the AC power source and the first and second
Connected to the series circuit of line filter capacitors
Normal mode noise detecting means, and the normal mode noise detecting means.
Normal mode noise detected by the mode noise detecting means
Normal mode noise current in response to the
Noise compensation current, and this noise compensation current
The normal mode noise current of the power converter is flowing.
And a noise compensation current supply circuit for supplying the
The noise compensating current supply circuit includes the smoothing capacitor.
Capacitors for one end of the first and second line filter
First current control element connected between the first and second interconnection points
Between the interconnection point and the other end of the smoothing capacitor.
At least one of the second current control elements connected therebetween.
One and the first and second current control elements are
-Normal mode detected by the normal mode noise detecting means
Supplying the noise compensation current in response to noise
The noise reduction device is characterized by
is there.

[0006]

According to the invention of each claim, a compensation current for canceling a noise component can be injected by the operation of one or both of the first and second current control elements. That is, noise can be reduced by the active filter operation. Therefore, according to the invention of each claim,
Compared with a filter based on a passive element such as a reactor, the size, cost, and performance of the noise reduction device can be reduced. According to the first aspect of the present invention, common mode noise can be easily and satisfactorily reduced.
According to the second aspect of the present invention, normal mode noise can be easily and satisfactorily reduced.

[0007]

First Embodiment Next, an inverter device according to a first embodiment will be described with reference to FIGS. The inverter device shown in FIG. 2 includes a bridge type full-wave rectifier circuit 3 connected to an AC power supply 1 via a line filter 2, and the rectifier circuit 3
Smoothing capacitor 4 connected between a pair of output terminals
And the three-phase inverter connected to the smoothing capacitor 4.
Data circuit 5. The line filter 2 is connected between a pair of AC power supply lines and connected in series to each other.
And second and third line filter capacitors C1, C2 and first and second reactors L1, L2 connected in series to a pair of AC power supply lines, respectively. The capacitors C1 and C2 are high-frequency capacitors having relatively low capacitance, and the reactors L1 and L2 have relatively small inductance.

The inverter circuit 5 comprises first and second switching elements Q1, Q2 each comprising an insulated gate field effect transistor having a source connected to a substrate.
2 is connected between a pair of DC power supply lines, and a series circuit of third and fourth switching elements Q3, Q4 and a series circuit of fifth and sixth switching elements Q5, Q6 are connected to a pair of DC power lines. This is a well-known three-phase bridge type inverter connected between power supply lines. The first to sixth switching elements Q1 to Q6 are on / off controlled by a PWM pulse supplied from the control circuit 7 in a known manner.

The three-phase output line of the inverter circuit 5 is shown in FIG.
1.5kW three-phase induction motor 6, schematically indicated by
Are connected to each phase winding. The electric motor 6 has a capacitance C between itself and the ground. Therefore, when the pulse-like voltage output from the inverter circuit 5 is applied to the electric motor 6, a leakage current, that is, a common mode noise current flows to the ground. The path of the leakage current on the power supply 1 side is
These are the ground capacitance (not shown) of the power supply 1, the connection point between the line filter capacitors C1 and C2 and the ground, and the straight capacitance of the AC power supply line.

The inverter shown in FIG. 2 has a noise reduction device comprising a leakage current detector 8 as noise detection means and a noise compensation current supply circuit 9. The leakage current detector 8 is a zero-phase CT including an annular core 13 made of ferrite, two primary windings n1a and n1b, and one secondary winding n2, and is formed by a difference between currents of a pair of power supply lines. A leakage current (zero-phase current component) Ise is detected. For this reason. Two one
The secondary windings n1a and n1b are connected in series to a pair of power supply lines between the AC power supply 1 and the rectifier circuit 3, respectively. The cross-sectional area of the core 13 is 50 mm ² and the primary winding n1
The number of turns of a, n1b and the secondary winding n2 is 10.

The noise compensating current supply circuit 9 includes first and second transistors Tr1 and Tr2 as first and second current control elements, and first and second diodes D1 and D2.
And a coupling capacitor Cb. The NPN first transistor Tr1 is connected between one end of the smoothing capacitor 4 and the iron core or frame or cover of the motor 6 via a coupling capacitor Cb having a capacitance of 1000 pF and a withstand voltage of 1 vK. I have. PNP-type second transistor Tr2
Is connected between the other end of the smoothing capacitor 4 and the iron core or frame or cover of the electric motor 6 via a coupling capacitor Cb. The first transistor Tr1 is of the NPN type, the second transistor Tr2 is of the PNP type, and
The second transistors Tr1 and Tr2 have polarities opposite to each other. The bases of the first and second transistors Tr1 and Tr2
The terminal (control terminal) is connected to one output line of the zero-phase current detector 8, and the interconnection point of the first and second transistors Tr1 and Tr2 is connected to the other output line of the zero-phase current detector 8. ing. Therefore, the first and second transistors T
r1 and Tr2 operate in opposite directions. The first and second diodes D1, D2 are first and second transistors Tr1, T2.
These are connected in anti-parallel to protect r2.
The first and second transistors Tr1, Tr2 high current gain, a high frequency, it is requested a high breakdown voltage, h _fe =
200, f _T = 140 μHz, V _CEO = ± 160 V. The cover of the electric motor 6 is connected to the ground by an earth wire.

Next, the operation of the inverter of FIG. 2 will be described. The AC voltage of the power supply 1 is rectified by the rectifier circuit 3. The output voltage of the rectifier circuit 3 is smoothed by the smoothing capacitor 4 and becomes the input voltage of the inverter circuit 5. The first to sixth switching elements Q1 to Q6 of the three-phase inverter circuit 5 are on / off controlled by a well-known PWM pulse. The three-phase induction motor 6 is driven by the output voltage of the inverter circuit 5.

As described with reference to FIG. 1, the capacitance C exists between the electric motor 6 as a load and the ground. Therefore, every time a voltage is applied from the inverter circuit 5 in a pulsed manner, a leakage current, that is, a zero-phase current Ic flows through the capacitance C.
The leakage current detector 8 detects a leakage current at the input line of the rectifier circuit 3, and detects the first and second transistors Tr1 and T1.
Drive r2. It is preferred that the leakage current detector 8, that is, the turns ratio N of the CT be smaller. There is a relationship of I01 = NI02 between the actual zero-phase current value I01 and the output current I02 of the leakage current detector 8. The output current I02 of the leakage current detector 8 is equal to the first and second currents.
When the current flows into the bases of the transistors Tr1 and Tr2, it is amplified by the transistors Tr1 and Tr2. When the first transistor Tr1 is ON, the smoothing capacitor 4 and the first
A noise compensation current flows through a closed circuit including the transistor Tr1, the coupling capacitor Cb, the capacitance C of the motor 6, and one of the lower switching elements Q2, Q4, Q6 of the inverter circuit 5, and the motor 6 leaks. The current, ie, the zero-phase current, is canceled. The current amplification factor of the first transistor Tr1 is h _fe
If compensation current Ic1 supplied through the first transistor Tr1 is h _fe I _02. Since I ₀₂ is the NI _01, Ic1 is expressed by the following equation. Ic1 = h _fe I ₀₂ = h _fe (NI ₀₁ ) The current I ₀₁ on the primary side of the leakage current detector 8 is expressed by the following equation. I ₀₁ = Ic -Ic1 = Ic -h _fe (NI ₀₁ ) Accordingly, the value of I ₀₁ is determined by the following equation. I ₀₁ = Ic / (1 + Nh _fe ) As is clear from this equation, when the value of Nh _fe is increased,
The current (leakage current component) I ₀₁ in the AC power supply line becomes smaller. Now, if N = 1 and h _fe = 100, then I ₀₁ = I c / 101, and the leakage current of the motor 6 can be reduced to 1/100 or less.

When the second transistor Tr2 is on,
Smoothing capacitor 4, one of the upper switching elements Q1, Q3, Q5 of inverter circuit 5, capacitance C of electric motor 6, coupling capacitor Cb, and second transistor T
The noise compensation current Ic1 flows in the closed circuit of r2. The noise reduction effect of this noise compensation current is due to the first transistor T
The same occurs when r1 is on. The noise reduction control system of FIG. 2 is a proportional control feedback system, and actively compensates for leakage current. Note that the coupling capacitor Cb
Is for DC cut, and is required for the withstand voltage test.

FIG. 3 shows the leakage current Ic and the compensation current Ic1 of FIG.
And the measured waveform of the current I0 of the ground line. As is clear from this, the leakage current can be reduced to 2% or less before compensation. Further, in the circuit of FIG. 2, since the Tr1 and Tr2 of the first and second transistors have opposite polarities, the output of one secondary winding n2 can control the two transistors Tr1 and Tr2. The configuration is simplified.

[0016]

Second Embodiment Next, an inverter device according to a second embodiment will be described with reference to FIG. However, in FIG. 4, substantially the same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. The inverter shown in FIG. 4 has a normal mode noise detector 8a and a noise compensation current supply circuit 9a for reducing normal noise. The normal mode noise detector 8a includes a transformer provided between the power supply 1 and the line filter 2, that is, a CT11 and a noise component extracting filter 12. CT11 includes first and second primary windings n1a connected in series to a pair of AC power supply lines,
n1b and the output winding n2 are wound around the annular magnetic core 13. The sum of the currents of the primary windings n1a and n1b is obtained in the output winding n2 of CT11. Normal mode noise flows in the same manner as normal current, so that noise current and normal current are distinguished by frequency. Since the power supply 1 is a commercial AC power supply and has a low frequency of, for example, 50 Hz, the filter 12 connected to the secondary winding n2 is
A frequency component higher than the frequency of the AC voltage is extracted.

One output line of the filter 12 is an NPN
Base of the first transistor Tr1 of the PNP type and the second transistor of the PNP type.
And the other output line is connected to the interconnection point of the first and second transistors Tr1 and Tr2.

The collector of the first transistor Tr1 is shown in FIG.
The collector of the second transistor Tr2 is connected to the upper terminal of the smoothing capacitor 4 in the same manner as
Connected to the lower terminal. The interconnection point of the first and second transistors Tr1 and Tr2 is connected to the interconnection point of the two capacitors C1 and C2 of the line filter 2.

The switching elements Q1 to Q6 of the inverter circuit 5 in FIG. 4 are turned on and off at a high frequency of, for example, about 20 kHz, as in FIG. In the circuit of FIG. 4, when the supply of the noise compensation current by the first and second transistors Tr1 and Tr2 is not performed, the normal mode is established by turning on and off the first to sixth switching elements Q1 to Q6. Noise occurs. Normal mode noise is
For example, the power supply 1, the reactor L1, the upper diode of the rectifier circuit 3, the upper switching element of the inverter circuit 5, the motor 6, the lower switching element of the inverter circuit 5, and the lower diode of the rectifier circuit 3. To the closed circuit of the reactor and the reactor L2. The reactors L1 and L2 have a function of suppressing high-frequency noise, but cannot remove all of the noise. Therefore, a noise current flows through the power supply 1. Therefore, in the circuit of FIG. 4, high-frequency normal mode noise is detected by the normal mode noise detector 8a, whereby the first and second transistors Tr1 and T2 are detected.
Drive r2. When the first transistor Tr1 is on, a compensation current for canceling the noise component is supplied.

[0020]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) By modifying the circuit of FIG. 2, the line filter 2 can be connected between the leakage current detector 8 and the rectifier circuit 3 as shown in FIG. (2) The power supply 1 of FIG.
Can be a three-phase bridge rectifier circuit, and the leakage current detector 8 can be a three-phase zero-phase current detector. (3) The switching elements Q1 to Q6 are bipolar transistors, and the transistors Tr1 and Tr2 are FETs.
And other current control elements. (4) The inverter circuit 5 can be a single-phase inverter circuit. (5) When only the noise component in one direction is suppressed, one of the first and second transistors Tr1 and Tr2 can be omitted. (6) The present invention can also be applied to a circuit that connects the midpoint of the three windings of the induction motor 6, that is, the midpoint of the three-phase load, to the ground.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a conventional inverter device.

FIG. 2 is a circuit diagram showing an inverter device according to a first embodiment of the present invention.

FIG. 3 is a waveform diagram showing a current of each part in FIG.

FIG. 4 is a circuit diagram showing an inverter device according to a second embodiment.

FIG. 5 is a circuit diagram showing an inverter device according to a modification.

[Explanation of symbols]

 5 Inverter circuit 6 Induction motor 8 Leakage current detector Tr1, Tr2 Compensation current supply transistor

Claims (2)

(57) [Claims] A rectifier circuit connected to an AC power supply;
A smoothing capacitor connected between a pair of DC output terminals of the rectifier circuit
Capacitor and the inverter connected to the smoothing capacitor.
A noise reduction device in a power conversion device for converting power based on ON / OFF of a switching element of the inverter circuit , wherein the load of the inverter circuit is reduced. Leakage current flowing from
To detect the current as a noise current.
And connected leak current detection means between the serial rectifier circuit, in response to the detected leakage current to form a compensation current of the leakage current in the opposite direction by said leakage current detection means, the compensation current the power and a compensation current supply circuit for supplying to the line flowing of leakage current of the converter, the compensation current supply
The circuit is between one end of the smoothing capacitor and ground.
Current control element connected to the
Second current control connected between the other end of the power supply and ground
And at least one of the first and second elements.
The current control element of
A noise reduction device for supplying the compensation current in response to a flow . Wherein a rectifier circuit connected to an AC power supply, a smoothing capacitor connected between a pair of DC output terminals of the rectifier circuit, which is connected to the smoothing capacitor inverter - a capacitor circuit, the AC Between the power supply and the rectifier circuit.
First and second line filters connected between force lines
And a line filter including a series circuit of
The switching element of the inverter circuit is turned on or off.
Noise in power converters that convert power based on
Noise reduction device, wherein the AC power supply and the first and second line filter
Normal mode connected between the capacitor and the series circuit
Noise detecting means, and a normal mode detected by the normal mode noise detecting means .
The normal mode noise in response to a mode noise current.
Noise compensation current in the opposite direction to the
The compensation current is supplied to the normal mode noise power of the power converter.
Supply circuit for noise compensation current supplied to the flowing line
A noise compensation current supply circuit,
And one end of the first and second line fills
A first capacitor connected between the
A current control element, the interconnection point and the smoothing capacitor.
Of the second current control element connected between the
And the first and second current controls
The element was detected by the normal mode noise detecting means.
A noise reduction device for supplying the noise compensation current in response to normal mode noise.