JP2006238582A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter for reducing a common mode current leaking from a reactor installed in the power converter and suppressing normal mode harmonic currents, fully suppressing common mode noise and eliminating adverse effects on the peripheral devices. <P>SOLUTION: The power converter is provided with the harmonics or harmonic currents for suppressing reactor at one among the input, the output and the interior. A frame of the reactor is insulated from the ground and connected to the ground via an impedance element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power conversion device that reduces common mode noise leaking from a reactor in a power conversion device including a reactor at an input, output, or inside.

  Conventionally, in order to reduce a normal mode harmonic current generated in a power conversion device, as shown in Patent Document 1, a reactor is inserted at an appropriate portion of a circuit of the power conversion device. FIG. 5 shows a power converter provided with the AC reactor shown in Patent Document 1. As shown in FIG.

  In FIG. 5, reference numeral 1 denotes an AC power source, which is connected to the rectifier circuit 3 through an AC reactor 2. The AC power supplied from the AC power source 1 is converted into DC power by the rectifier circuit 3 and smoothed by the capacitor 4. The DC power smoothed by the capacitor 4 is converted into AC power by the inverter circuit 5 and supplied to a load 6 such as an induction motor. The AC reactor 2 suppresses the harmonic current in the normal mode that flows through the AC power supply 1 in accordance with the switching operation of the power converter. The rectifier circuit 3 may be a voltage-type PWM rectifier circuit using a switching element instead of a diode rectifier circuit.

  Further, as shown in FIG. 6, there is already known a power conversion device in which a DC reactor 7 is provided in the DC side circuit of the rectifier circuit 3 instead of the AC reactor 2 to reduce the harmonic current flowing in the AC power supply 1. It has been.

  In such a conventional power converter, as shown by the dotted lines in FIGS. 5 and 6, the induction motor 6 has a floating capacitance 6a between each winding and the frame. Since the frame of the induction motor 6 is grounded to the ground, a high-frequency common mode noise current leaks to the ground through the floating capacitance 6a as the switching element in the inverter circuit 5 is turned on / off. This causes inconveniences that cause malfunctions in the devices.

  In order to suppress such common mode leakage current, a common mode choke, a common mode transformer, or the like has been conventionally inserted into the output of the power converter, or a common mode voltage or current as disclosed in Patent Document 1 is applied. An active common noise canceller or the like that suppresses a common mode leakage current by injecting a voltage or a current that is detected and cancels out into the output circuit of the power converter is used.

  FIG. 7 is an example of a conventional power converter using the active common noise canceller disclosed in Patent Document 1.

In FIG. 7, reference numeral 8 denotes a common mode current detector configured to detect common mode noise constituted by a zero-phase current transformer, and reference numeral 9 denotes a complementary transistor circuit, which is detected by the common mode current detector 8. This is a compensation circuit that generates a compensation current having a phase opposite to that of the mode current and injects it into the ground circuit of the induction motor 6 via the coupling capacitor C9. The common mode current leaking from the load induction motor 6 to the ground is detected by the common mode current detector 8, and a compensation current − having a phase opposite to that of the current is detected by the compensation circuit 9 according to the detected common mode current Iz. Iz is formed and injected into the ground circuit. Thereby, the common mode leakage current Iz is canceled by the compensation current −Iz, and the common mode leakage current is suppressed.
Japanese Patent Laid-Open No. 9-266677

  By providing a common mode leakage current suppression means such as an active common noise canceller in the power converter as described above, it is possible to suppress a common mode leakage current leaking from a load such as an induction motor. If the reactor frame inserted at an appropriate location in the circuit for suppression is grounded, the common mode current also leaks through the stray capacitance between the reactor winding and the frame. For example, in the case of FIG. 7, the common mode current leaking from the reactor itself may be the common mode on the path from the frame of the reactor 2 to the power source 1 even if a common mode leakage current suppressing means such as an active common noise canceller is provided. The current cannot be suppressed. For this reason, in the power converter device having the normal mode harmonic current suppressing reactor, the common mode leakage current cannot be sufficiently suppressed, and there is an inconvenience that adversely affects peripheral communication devices and the like.

  In order to improve such an inconvenience, the present invention reduces common mode current leaked from a reactor for suppressing normal mode harmonic current installed in a power converter, and sufficiently suppresses common mode noise. It is an object of the present invention to provide a power conversion device that does not adversely affect other devices.

  In order to solve such a problem, the present invention provides a power conversion device including a reactor for suppressing harmonics or high-frequency current at least at an input, an output, or an inside thereof, and the reactor frame is insulated from the ground. The frame is grounded via an impedance element.

  In the present invention, a resistance element can be used as the impedance element.

  According to the present invention, after the reactor frame provided in the power converter is insulated from the ground, the capacitance is suspended in the reactor winding by connecting the frame to the ground via the impedance element. The resonance frequency of the common mode current that leaks to the ground via the IC shifts to a different frequency due to the inserted impedance element, so the magnitude of the high-frequency noise current that has had an adverse effect on peripheral devices is significantly suppressed. And adverse effects on peripheral devices can be eliminated.

  In addition, when a resistance element is used as the impedance element, the magnitude of the common mode current leaking to the ground via the floating capacitance of the reactor winding can be reduced by this resistance element, and at the same time, the attenuation of this current can be reduced. Since it can be accelerated, it does not affect peripheral devices.

  Embodiments of the present invention will be described based on examples shown in the drawings.

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

  In FIG. 1, reference numeral 1 denotes an AC power source, and a rectifier circuit 3 is connected to the AC power source 1 via an AC reactor 20. The AC power supplied from the AC power source 1 is converted into DC power by the rectifier circuit 3, and the converted DC power is smoothed by the capacitor 4 and supplied to the inverter circuit 5. The inverter circuit 5 converts the AC power to variable frequency AC power. It is converted and supplied to the induction motor 6.

  This configuration is shown except for the compensation circuit 9 and the like of the conventional apparatus shown in FIG. 7, and the reactor 20 suppresses the harmonic current in the normal mode that is generated by the switching operation of the switching element of the inverter circuit 5. However, it does not affect the suppression of the common mode current that leaks to the ground via the floating electrostatic capacitance 20a of its winding.

  In the present invention, the frame 21 of the reactor 20 is insulated from the ground E in order to suppress the common mode leakage current that leaks through the floating capacitance 20a of the winding of the reactor 20, and between the frame 21 and the ground E The impedance element 9 is connected to the ground and the frame 21 of the reactor 20 is grounded via the impedance element 10.

  When the frame 21 of the reactor 20 is grounded via the impedance element 10, the capacitance or inductance of the added impedance element 10 is added to the internal capacitance C and the internal inductance L in the leakage circuit of the reactor 20. Since the value is changed, the resonance frequency of the leakage circuit is changed. If the resonance frequency when the impedance element 10 is not connected is f0, the common mode current having the frequency f0 is increased. When the impedance element 10 is connected, the resonance frequency shifts to f10, so that the common mode current at the frequency f10 increases and the common mode current at the frequency f0 is significantly reduced. The impedance element 10 may include not only capacitance and inductance but also resistance.

  Therefore, when the frequency f0 before connection of the impedance element 10 is in a radio frequency band, for example, this band is selected by appropriately selecting the inductance or capacitance value of the impedance element 10 connected to the ground circuit of the reactor 20. The frequency f10 that does not affect a radio device such as a radio that is out of the range can be set, and noise interference to a radio device such as a nearby radio device can be suppressed.

  In the second embodiment of the present invention shown in FIG. 2, a DC reactor 70 is inserted on the DC side of the rectifier circuit 3. Also in this embodiment, the frame 71 of the DC reactor 70 is insulated from the ground E, and the frame 71 is connected to the ground E via the impedance element 11.

  Similarly to the first embodiment, the frequency of the resonance point current of the common mode current that leaks to the ground E through the floating capacitance 70a of the winding of the reactor 70 is also connected to the impedance element 11 in the second embodiment. Therefore, it is possible to suppress the common mode current of the frequency f0 that is harmful to the wireless device or the like. Naturally, the inductance or capacitance value of the impedance element is selected so that the frequency f11 is a frequency that does not affect the wireless device.

  In the third embodiment shown in FIG. 3, the frame 21 of the AC reactor 20 inserted on the AC side of the rectifier circuit 3 is insulated from the ground E, and instead of the impedance element between the frame 21 and the ground E. The resistance element 12 is connected.

  In this case, although the resonance frequency of the leakage circuit of the reactor 20 cannot be changed greatly, the magnitude of the leaked common mode current can be reduced, and at the same time the attenuation of the vibration can be accelerated, and the resistance of the resistance element 11 By appropriately selecting the value, it is possible to make the size so as not to affect the peripheral device.

  In the fourth embodiment shown in FIG. 4, a frame 71 of a DC reactor 70 inserted on the DC side of the rectifier circuit 3 is insulated from the ground E, and a resistance element 13 is provided between the frame 21 and the ground E instead of the impedance element. Are connected.

  In this case, although the resonance frequency of the leakage circuit of the reactor 20 cannot be changed greatly, the magnitude of the leaked common mode current can be reduced, and at the same time, the attenuation of the vibration can be accelerated, and the resistance of the resistance element 13 can be reduced. By appropriately selecting the value, it is possible to make the size so as not to affect the peripheral device.

1 is a circuit configuration diagram showing a first embodiment of the present invention; It is a circuit block diagram which shows the 2nd Example of this invention. It is a circuit block diagram which shows 3rd Example of this invention. It is a circuit block diagram which shows 4th Example of this invention. It is a circuit block diagram which shows a conventional apparatus. It is a circuit block diagram which shows another conventional apparatus. It is a block diagram which shows another conventional apparatus.

Explanation of symbols

1: AC power source 20: AC reactor 3: Rectifier circuit 4: Capacitor 5: Inverter circuit 6: Induction motor 70: DC reactor 10, 11: Impedance element 12, 13: Resistance element

Claims (2)

  A power converter having a reactor at least at any one of an input, an output, and an inside thereof, wherein the reactor frame is grounded through an impedance.   2. The power converter according to claim 1, wherein a resistor is used as the impedance.

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