JP2003235269A - Noise reducing apparatus for power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a noise current flowing through a power converter more simply and inexpensively than by a conventional circuit. <P>SOLUTION: In the power converter consisting of a rectification circuit 2 connected to an AC power source 1, and a smoothing capacitor C<SB>0</SB>and an inverter circuit 3 which are connected to the DC output of the circuit 2, for example, a serial circuit consisting of a reactor L<SB>1</SB>and a capacitor C<SB>1</SB>is connected between the negative pole side of e.g. an AC output terminal and a ground G so that an impedance can have the extremely small value in a resonant frequency determined by the inductance of the reactor L<SB>1</SB>and the capacitance of the capacitor C<SB>1</SB>, thereby bypassing more common mode currents. In this way, the apparatus which is simpler, smaller and lower-cost than a conventional apparatus using a serial circuit of an MOSFET can be realized. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for reducing noise current (simply referred to as noise) in a power conversion device such as an inverter device.

[0002]

2. Description of the Related Art FIG. 11 shows a conventional example of this kind. this
Is a system that drives a 3-phase induction motor with a 3-phase inverter.
A conventional example of a noise reduction device applied to a stem is also shown.
Of. That is, the input of the rectifier 2 to the AC power supply 1 is
The output of the rectifier 2 is connected to the capacitor via the input of the current detector 5.
Sensor C₀But capacitor C₀Semiconductor switch Q₁~ Q₆Yo
Inverter 3 is composed of
The motor 4 has a capacitor C for the AC power supply 1.₂And C₃In series
Each circuit is connected. Also, N channel M
OSFET (metal oxide film type field effect transistor) FE
T₁And FET₂Are connected in series to form a capacitor C₀Parallel with
The output of the current detector 5 is FET₁And FET₂With the gate of
Resistance R between each source₁, R₂Through FET₁of
Source and FET₂The drain is the capacitor C₁Through
Ground (G) G, capacitor C₂And C ₃Connect the connection point of
Each is connected to the ground G.

The FETs ₁ and ₂ are used as amplifiers here, and the leakage current (leakage current) detected by the current detector 5 by the FETs ₁ and ₂ and the capacitor C _1.
Accordingly, a current supply circuit 6 for supplying a current of opposite phase to this to the power line in which the leakage current of the power conversion device is flowing is formed.

The operation of FIG. 11 will be described. The switches Q ₁ to Q ₆ of the three-phase inverter circuit 3 are on / off controlled by a PWM (pulse width modulation) pulse, and the motor 4 is driven by the output voltage of the inverter circuit 3. There is a capacitance C between the motor 4 and the ground G. Therefore, every time a voltage is applied in a pulsed manner from the inverter circuit 3, a leakage current i _c (= C · dv / dt) flows through the electrostatic capacitance C. The current detector 5 detects a leak current flowing through the motor 4 and a capacitance C (not shown), and drives the FET ₁ or the FET ₂ . The output voltage v _G1 (v _G2 ) of the current detector 5 is FE
When applied to the gate of T ₁ (FET ₂ ), this voltage v _G1
A current i _c1 corresponding to (v _G2 ) flows through FET ₁ (FET ₂ ). It indicates the current waveform at this time _{(i c, i c1, i} E) is a diagram 12.

For example, when the leakage current i _c flows in the direction of the arrow in FIG. 11, the primary winding 5a of the current detector 5 has i
_c ′ flows, and the voltages v _{G 1} and v _G2 are generated in the secondary windings 5b and 5c of the current detector 5. Then, FET ₂ turns on,
I _c1 flows through the capacitor C ₁ . As a result, most of the leakage current i _c flows as i _c1 and i _E (= i _c −i _c1 )
Is reduced, and the noise voltage (noise terminal voltage) is also reduced. When the direction of the leakage current i _c is opposite to the above, the voltages v _G1 and v _G2 generated in the secondary windings 5b and 5c of the current detector 5
Is reversed and FET ₁ is turned on, and a current i _{c1 in the} opposite direction to the above flows through the capacitor C ₁ . Also in this case, most of the leakage current i _c flows as i _c1 and i _E (= i _c −
i _c1 ) is reduced, and the noise voltage (noise terminal voltage) is also reduced.

[0006]

The circuit configuration of FIG. 11 has problems 1) and 2). 1) The current of the common mode component is output to the output side of the current detector regardless of the frequency band. Therefore, the MOSFET is driven by the output of this detector, and a current flows between the drain and the source. Generally, the frequency component of the leakage current is in the range of several hundred kHz to several MHz,
For the purpose of reducing the leakage current, it is only necessary to detect the current in the above frequency band. However, for example, if a component such as a three-phase unbalanced current is detected and output, the extra current will flow into the noise current reduction circuit, resulting in a large MOSFET loss and the use of an element with a large allowable loss. Will not happen.

2) MOSFET between terminals of DC intermediate circuit
Since a series circuit of is connected, if both MOSFETs are turned on at the same time due to the influence of external noise, etc.
A short-circuit current will flow through the SFET, and in the worst case, the MOSFET will be damaged. Therefore, an object of the present invention is to provide a highly reliable noise reduction device that is not affected by a three-phase unbalanced current, has a small number of components, and is low in cost.

[0008]

In order to solve such problems, in the invention of claim 1, a smoothing circuit and an inverter circuit are connected to a rectifier circuit connected to an AC power source and the DC output of this rectifier circuit. In the power converter configured as described above, a series circuit of a capacitor and an impedance element is connected between at least one of the DC output terminals of the rectifier circuit and the ground terminal.

According to the second aspect of the present invention, the rectifier circuit connected to the AC power source, and the DC output of the rectifier circuit are connected to the DC output of the rectifier circuit. A series connection circuit of at least two capacitors having the same capacitance is connected between the output terminals, and an impedance element is connected between the intermediate point of the series connection circuit and the ground terminal.

According to another aspect of the present invention, the rectifier circuit connected to the AC power source and the power converter configured by connecting the DC output of the rectifier circuit to the smoothing circuit and the inverter circuit are input to the rectifier circuit. It is characterized in that a series connection circuit of at least two capacitors having the same capacity is connected between each terminal of the section, and an impedance element is connected between the intermediate point of this series connection circuit and the ground terminal.

That is, by appropriately configuring the impedance element, the impedance of the path is reduced in a specific frequency band, the effect of bypassing the common mode noise current is increased, and the noise current on the power supply side can be reduced. Therefore, it is possible to significantly reduce noise in the frequency band most desired to be reduced. Whatever the configuration of the impedance element, the noise reduction amount in the specific frequency band can be made almost the same as that of the configuration using the switching element such as MOSFET with a simple configuration, so that the size and the cost can be reduced. . In addition, the direct current middle part is MOS
Since switching elements such as FET are not used,
The reliability can be significantly improved.

[0012]

1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a circuit diagram showing a first concrete example thereof, and FIG. 3 is a circuit showing a second concrete example thereof. FIG. 4 is a circuit diagram showing a third concrete example thereof, and FIG. 5 is a circuit diagram showing a fourth concrete example thereof. The examples shown in FIG. 1 to FIG. 5 are, for example, the negative electrode side of the DC output terminal of the rectifier 2 and the ground G.
A characteristic is that a series circuit of a capacitor C ₁ and an impedance element Z ₁ is connected between and. An example of the impedance element Z ₁ is shown in FIG. 6, FIG. 2 is shown in FIG. 6 (b), FIG. 3 is shown in FIG. 6 (e), and FIG. 4 is shown in FIG. 6 (g). 5 can be said to be an example using each of those shown in FIG. In these examples, the series circuit of the capacitor C ₁ and the impedance element Z ₁ is connected between the DC output terminal, for example, the negative electrode side and the ground G, but the DC output terminal, for example, the positive electrode side and the ground G is connected. Alternatively, it may be connected between the positive electrode side and the negative electrode side.

The functions and operations of the concrete examples shown in FIGS. 2 to 5 will be described. For Figure 2, the capacitance c ₁ of inductance l ₁ and the capacitor C ₁ of the reactor L ₁
Resonance frequency f = 1 / [2π√ (l ₁ ·
In c ₁ )], the impedance is minimized, and a large amount of common mode current is thereby bypassed. To explain its effect in an easy-to-understand manner,
It is FIG. The attenuation characteristic indicated by the one-dot diagonal line is the capacitor C ₁
If the amount of attenuation is only due to
In this case, the resonance characteristic of the reactor L ₁ and the capacitor C ₁ increases the amount of attenuation as indicated by the shaded area near the resonance frequency f.

FIG. 3 shows a resistance R ₁ in addition to that shown in FIG.
Are connected in series. By doing so, the common mode noise current itself is attenuated, and the amount of attenuation as a filter is further increased. Also, due to the current flowing through the common mode noise current path,
As a result, there is also an effect of suppressing the noise component that increases. Figure 8
Shows the damping characteristics. The dotted line in the figure is the attenuation characteristic in the case of FIG. The noise component which increases as a result is shown by N, and it can be seen that this component N is suppressed as shown by the dotted line as compared with the case of FIG.

In FIG. 4, the primary side of the transformer Tr ₁ is connected in place of the reactor L _{1 of} FIG. 2 and the secondary side is short-circuited. In this configuration, at the resonance frequency f = 1 / [2π√ (l ₂ · c ₁ )] determined by the leakage inductance l ₂ of the transformer Tr ₁ and the capacitance c ₁ of the capacitor C ₁ , the impedance becomes minimum, which Many common mode currents are bypassed. The operation is the same as that of FIG. 2, but the leakage inductance value has little frequency dependence, and therefore, there is an advantage that the characteristics are easy to manage. In FIG. 5, R ₁ is connected to the secondary side of the transformer Tr ₁ of FIG. 4 to attenuate the common mode noise current itself and to provide an effect. The other points are the same as in the case of FIG.

FIG. 9 is a circuit diagram showing a second embodiment of the present invention. This is to connect a series connection circuit of at least two capacitors C ₄ and C ₅ having the same capacity between the DC output terminals of the rectifier circuit 2, and to connect an impedance element between the midpoint P of this series connection circuit and the ground terminal G. Z ₁ is connected, and is functionally the same as that shown in FIG. The capacitors C ₄ and C ₅ may have the same capacity, and two or more capacitors can be used. FIG. 10 is a circuit diagram showing a third embodiment of the present invention. This is because at least two capacitors C having the same capacitance are provided between the terminals of the input section of the rectifier circuit 2.
A series connection circuit of C ₄ and C ₅ is connected, and an impedance element Z _{1 is provided} between the intermediate point P of this series connection circuit and the ground terminal G.
, Which is also functionally the same as that shown in FIG.

That is, the circuit shown in FIG. 2 is the same as that shown in FIG. Further, in the case of the multi-phase input shown in FIG. 3, the circuit configuration becomes complicated accordingly, while in FIG.
Since the DC intermediate circuit does not change even if it is a multi-phase input, the structure shown in FIG. 2 can simplify the structure.

[0018]

According to the present invention, with a simple structure,
Since the noise reduction amount in the specific frequency band can be made almost equal to that of the configuration using the switching element such as MOSFET, the cost and the size can be reduced. Further, since the switching element such as MOSFET is not used in the DC intermediate portion, the reliability can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a first specific example of the first embodiment.

FIG. 3 is a circuit diagram showing a second specific example of the first embodiment.

FIG. 4 is a circuit diagram showing a third specific example of the first embodiment.

FIG. 5 is a circuit diagram showing a fourth specific example of the first embodiment.

FIG. 6 is an explanatory diagram showing an example of an impedance element.

FIG. 7 is a diagram for explaining the operation of FIG.

FIG. 8 is an explanatory view of the operation of FIG.

FIG. 9 is a circuit diagram showing a second embodiment of the present invention.

FIG. 10 is a circuit diagram showing a third embodiment of the present invention.

FIG. 11 is a circuit diagram showing a conventional example.

FIG. 12 is a waveform chart showing currents at respective portions in FIG. 11.

[Explanation of symbols]

1 ... AC power supply, 2 ... rectifier, 3 ... inverter circuit, 4 ...
Motor, 5 ... Current detector, 5a ... Primary winding, 5b, 5c
... secondary winding, 6 ... current supply circuit, Z ₁ ... impedance element, L ₁ ... reactor, C _{0 to} C ₄ ... capacitor, R ₁ ,
R ₂ ... Resistor, TR ₁ ... Transformer, FET ₁ , FET ₂ ... N
Channel MOSFET (metal oxide type field effect transistor).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Seiki Igarashi             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Satoshi Takizawa             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 5H007 AA01 BB06 CA01 CB02 CB05                       DA03 DA06 FA14

Claims (3)

[Claims] 1. A power converter comprising a rectifier circuit connected to an AC power source and a DC output of the rectifier circuit connected to a smoothing circuit and an inverter circuit, and at least one of DC output terminals of the rectifier circuit. A noise reduction device for a power conversion device, wherein a series circuit of a capacitor and an impedance element is connected between a ground terminal and a ground terminal. 2. A rectifier circuit connected to an AC power source, and a power converter configured by connecting a DC output of the rectifier circuit to a smoothing circuit and an inverter circuit, wherein a capacitance is provided between the DC output terminals of the rectifier circuit. A series connection circuit of at least two capacitors of the same type is connected, and an impedance element is connected between an intermediate point of the series connection circuit and a ground terminal. 3. A rectifier circuit connected to an AC power source, and a power converter comprising a DC output of the rectifier circuit connected to a smoothing circuit and an inverter circuit. A noise reduction device for a power conversion device, wherein a series connection circuit of at least two capacitors having the same capacity is connected to, and an impedance element is connected between an intermediate point of the series connection circuit and a ground terminal.