JP2017060265A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device which is configured by connecting a plurality of semiconductor power converters in parallel and in which a common mode core is magnetically coupled to an output of each semiconductor power converter, and configured to reduce inductance when noise current in the same direction flows in each of the semiconductor power converters like electromagnetic interference noise current, and keep the inductance high when cross current flows between the semiconductor power converters.SOLUTION: In the power conversion device comprising the plurality of semiconductor power converters connected in parallel, common mode cores are magnetically coupled to respective output conductors of the semiconductor power converters, and a secondary conductor is made to penetrate commonly through these common mode cores, and both the ends of the secondary conductor are coupled to form a closed circuit of the secondary conductor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device that suppresses noise and cross current generated in a plurality of semiconductor power converters used in parallel connection.

  In a semiconductor power converter using a semiconductor element as a power conversion element, in particular, when a SiC semiconductor element using a SiC (silicon carbide) base material is used as the power conversion element, the semiconductor element operates at high speed. Magnetic Interference) is likely to generate noise, which often causes electromagnetic interference to other electronic devices.

  As an example of the countermeasure, Patent Documents 1 and 2 propose to suppress noise current by providing a common mode choke coil configured by magnetically coupling a common mode core to an input / output conductor of a semiconductor power converter. Has been.

  From the viewpoint of noise suppression, the larger the inductance of the common mode core (common mode choke coil), the higher the suppression effect, but there is a disadvantage that the generation loss of the common mode core expressed by the following equation (1) increases.

Loss of common mode core = 1/2 x L x I ² (1)
Here, L is the inductance of the common mode core, and I is the common mode (zero phase) current.

  Therefore, in practice, it is common to reduce the inductance L of the common mode core and prevent magnetic saturation in the core by forming a gap in the common mode core.

  As a method for increasing the capacity of a semiconductor power converter, there is a method of using a plurality of semiconductor power converters connected in parallel. This method is shown in Patent Document 3.

  When semiconductor power converters are connected in parallel, the characteristics of semiconductor switch elements such as IGBTs (insulated gate bipolar transistors) that make up the power converter are made uniform and the lengths of connecting conductors such as bus bars to be connected By making the connection lines uniform, the inductance of the connection line is made uniform, and the same gate pulse is used for the gate signal, so that a plurality of semiconductor power converters are operated as if they were one power converter. However, in practice, the switching timing of the semiconductor switch elements can be accurately adjusted because of the delay variation of the logic circuit of the control device in each semiconductor power converter and the phase shift of the synchronization clock signal. This is not possible, and the switching timing is shifted, so that a so-called cross current occurs in which a current flows from one power converter to the other power converter. This cross current becomes a current that short-circuits the DC power supply and becomes excessive, which may cause the semiconductor switch element constituting the power converter to burn out.

  As a countermeasure to prevent burning of the semiconductor switch element of the semiconductor power converter due to the cross current, the common mode core is magnetically coupled to the output circuit of the power converter, and the inductance of the common mode core is reduced by the function of the common mode core when the cross current is generated. In order to suppress the cross current, the conventional method is also used.

  FIG. 4 shows an example of a conventional power converter having a parallel configuration provided with such a cross current suppressing device using a common mode core.

  In FIG. 4, the semiconductor power converters 1 and 2 are formed of IGBTs, convert DC power supplied from the DC power source E into AC power or DC power, and supply the power 5 in parallel. Common mode cores 3 and 4 are provided in the output circuits of the power converters 1 and 2, respectively. The common mode cores 3 and 4 are formed of ring-shaped ferrite cores, and are magnetically coupled to the output conductors 1a and 2a by passing all three-phase AC output conductors of the power converters 1 and 2 through the hollow portions. Is done. Thereby, it becomes the structure which inserted the common mode choke coil in the output circuit of the power converters 1 and 2, respectively.

  When the three-phase output currents of the power converters 1 and 2 are balanced, the combined magnetic flux in the common mode cores 3 and 4 becomes zero. Therefore, the common mode cores 3 and 4 are used as inductances, that is, choke coils. Does not work.

  For example, when a common mode noise current flows from the power converters 1 and 2 to the load 5, or as indicated by a dotted arrow in FIG. 5, the output current of the power converter 1 does not pass through the load 5 and power When flowing in the converter 2 as the cross current Ic, the three-phase current flowing through the common mode cores 3 and 4 becomes unbalanced.

  In the cross current Ic, the switching operations of the semiconductor power conversions 1 and 2 are out of synchronization. For example, the IGBT Q11 connected to the positive electrode P side of the DC power supply E constituting the power converter 1 is turned on, and the DC of the power converter 2 is turned on. When the IGBT Q22 connected to the negative electrode N side of the power supply E is turned on, a load is applied on the positive electrode P-IGBTQ11-common mode core 3-common mode core 4-IGBTQ22-DC power supply E negative electrode N path of the DC power supply E It flows without going through 5.

  When such noise current or cross current is generated, the output currents of the power converters 1 and 2 become unbalanced. When an unbalanced current is generated, a magnetic flux is generated in the common mode cores 3 and 4 by the zero-phase current (common mode current). Therefore, the common mode cores 3 and 4 act as inductances, that is, choke coils, and noise. Current and cross current can be suppressed.

Japanese Patent No. 4351916 Japanese Patent No. 4260110 Japanese Patent No. 3676056

  However, in a power converter configured by connecting a plurality of semiconductor power converters in parallel, when a common mode core is magnetically coupled to the output of each semiconductor power converter, the inductance of the common mode core is equal to the common mode noise. There is a conflicting demand that it is desirable to keep the current low and the cross current high, and a countermeasure has been desired.

  In order to meet such demands, the present invention provides a power converter configured by connecting a plurality of semiconductor power converters in parallel, and magnetically couples a common mode core to the output of each of the semiconductor power converters. The common mode core reduces the inductance when a noise current in the same direction flows through each of the semiconductor power converters as an electromagnetic interference noise current, and reduces the inductance when a cross current flows between the semiconductor power converters. It is an object of the present invention to provide a power conversion device that can be kept high.

  In order to solve the above-described problems, the present invention provides a power conversion device configured by connecting a plurality of semiconductor power converters in parallel, and magnetically coupling a common mode core to an output conductor of each of the semiconductor power converters. These common mode cores are commonly provided with a secondary conductor penetrating, and both ends of the secondary conductor are coupled to form a closed circuit of the secondary conductor.

  In the present invention, an appropriate resistor can be inserted in series in the closed circuit formed by the secondary conductor.

  According to the present invention, in the power conversion device configured by connecting a plurality of semiconductor power converters in parallel, the secondary conductor penetrates the common mode core magnetically coupled to the output conductor of each semiconductor power converter. When a common mode current flowing in the same direction flows through each semiconductor power converter like an electromagnetic interference noise current by providing a secondary circuit that is closed by closing both ends of the secondary conductor, a common mode core When the cross current flows between the semiconductor power converters, the inductance of the common mode core can be kept high. For this reason, since it is not necessary to take measures to reduce inductance such as providing a gap in the middle of the common mode core, an effect of reducing the cost of the apparatus can be obtained.

The block diagram which shows the state in which the noise current of 1st Example of this invention is flowing. The block diagram which shows the state in which the cross current of 1st Example of this invention is flowing. The block diagram which shows the 2nd Example of this invention. The block diagram which shows the conventional power converter device. Operation | movement explanatory drawing of the conventional power converter device.

  Embodiments of the present invention will be described with reference to the embodiments shown in the drawings.

  FIG. 1 shows the configuration of the first embodiment of the present invention. In FIG. 1, reference numerals 1 and 2 denote semiconductor power converters that convert DC power supplied from the DC power supply E into AC power and supply the AC power to the load 5 in parallel. Reference numerals 3 and 4 denote common mode cores made of ring-shaped ferrite, and these output conductors 1a and 2a pass through the three-phase output conductors 1a and 2a of the power converters 1 and 4 in common. Are magnetically coupled to each other. The common mode cores 3 and 4 are pierced by a secondary conductor 6 in common, and the secondary conductor 6 joins both ends to form one closed circuit.

  In the power converter configured as described above, the semiconductor power converters 1 and 2 operate normally, and neither the common mode noise current In nor the cross current Ic due to electromagnetic interference noise flows through the semiconductor power converters 1 and 2. , The three-phase output current flowing through the common mode cores 3 and 4 is balanced, so that no common mode current is generated when flowing through the common mode cores 3 and 4. For this reason, since the magnetic flux by a common mode current does not generate | occur | produce in the common mode cores 3 and 4, the common mode cores 3 and 4 do not act as an inductance, and a loss does not generate | occur | produce.

  As shown in FIG. 1, when electromagnetic interference noise occurs in the power converters 1 and 2, the common mode noise currents In1 and In2 are supplied to the load 5 through the output conductors 1a and 2a of the power converters 1 and 2 as a result. Flowing. The common mode noise currents In1 and In2 are currents in the same direction as indicated by arrows.

  The secondary conductor 6 penetrated in common to the common mode cores 3 and 4 penetrates both cores in the same direction. That is, the front end of the secondary conductor 6 that penetrates the common mode core 3 from the power converter 1 side to the load 5 side passes through the other common mode core 4 from the power converter 2 side to the load 5 side and is coupled to the rear end. And a closed circuit is formed.

  When the common mode noise currents In1 and In2 flowing through the output conductors 1a and 2a of the converters 1 and 2 flow through the common mode cores 3 and 4, the secondary conductor 6 passing through the common mode cores 3 and 4 has this Since the secondary current indicated by the arrows I21 and I22 in the direction opposite to the common mode noise currents In1 and In2 flows, the magnetic flux generated in the common mode cores 3 and 4 by the secondary currents I21 and I22 is changed to the common mode noise current In1. , In2 cancels out the magnetic flux generated by In2. For this reason, the inductance with respect to the common mode noise current In1 and In2 of the common mode cores 3 and 4 can be reduced.

  On the other hand, as shown in FIG. 2, when a cross current Ic flows between the semiconductor power converters 1 and 2 via the output conductors 1a and 2a, in the common mode cores 3 and 4, as shown by arrows, The directions of the cross currents Ic flowing through are opposite to each other. Therefore, a secondary current I23 in the direction indicated by the arrow I23 is induced in the secondary conductor 6 in the portion passing through the common mode core 3, and the secondary current in the direction indicated by the arrow I24 in the portion passing through the common mode core 4. A current I24 is induced. Since the secondary currents I23 and I24 induced in the secondary conductor 6 are opposite in direction, they cancel each other, and the secondary current I2 flowing through the secondary conductor 6 becomes zero. 4 is maintained without being reduced. For this reason, the common mode cores 3 and 4 can maintain high inductance with respect to the cross current Ic.

  As in the present invention, in a power converter configured by connecting a plurality of semiconductor power converters in parallel, a common mode core is magnetically coupled to the output conductor of each semiconductor power converter, and these common mode cores are connected to each other. By penetrating the secondary conductor in common and forming a closed circuit with this secondary conductor, the common mode core inductance is reduced for common mode noise current, and the common mode core inductance for cross current. Can be maintained and not reduced. Accordingly, it is not necessary to previously reduce the inductance value by providing a gap in the common mode core, and the inductance value of the common mode core can be automatically adjusted in each mode.

  FIG. 3 shows a second embodiment of the present invention. The second embodiment is in series with a closed circuit formed by a secondary conductor 6 common to a plurality of common mode cores 3 and 4 magnetically coupled to output conductors of a plurality of semiconductor power converters 1 and 2, respectively. The point which inserted the resistor 7 differs from the said Example 1. FIG.

  In the second embodiment, when the common mode noise currents In1 and In2 flow from the power converters 1 and 2 to the load 5, the secondary current induced in the secondary conductor 6 in the common mode cores 3 and 4 Since I21 and I22 are added in the same direction, power is consumed by the combined current of currents I21 and I22. This power passes through the secondary circuit, that is, the common modes 3 and 4 in common, from the output conductors 1a and 2a side of the primary circuit of the common mode cores 3 and 4, that is, the main circuit of each power converter 1 and 2. By being supplied to the secondary conductor 6, energy of zero-phase current is consumed. Since the power consumption of the resistor 7 is obtained by multiplying the square of the current flowing through the resistor 7 by the resistance value of the resistor 7, the energy of the zero-phase current is appropriately processed by appropriately selecting the resistance value. Therefore, the noise suppression effect can be adjusted.

  When a cross current occurs, the secondary currents induced in the secondary conductors 6 penetrating the common mode cores 3 and 4 cancel each other, and the secondary current in the closed circuit of the secondary conductor 6 is not Since it does not flow, power consumption by the resistor 7 does not occur.

E: DC power source 1, 2: Semiconductor power converter 1a, 2a: Output conductor of semiconductor power converter 3, 4: Common mode core 5: Load 6: Secondary conductor 7: Resistor

Claims (2)

  In a power conversion apparatus configured by connecting a plurality of semiconductor power converters in parallel, a common mode core is magnetically coupled to an output conductor of each of the semiconductor power converters, and a secondary conductor is shared by these common mode cores. The power converter is characterized in that a closed circuit of the secondary conductor is formed by connecting both ends of the secondary conductor.   The power converter according to claim 1, wherein an appropriate resistor is inserted in series in a closed circuit formed by the secondary conductor.

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