JP2009296756A - Power conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a common mode current flow into a loop circuit comprising a parasitic capacitor cp3 between a primary-side coil 20a and a secondary-side coil 20b of a transformer 20 of a DCDC converter CV, parasitic capacitors cp1, cp2 between a primary-side coil and a secondary-side coil of a pulse transformer PT, and a ground line GL. <P>SOLUTION: A middle point tap mt at the primary side of the pulse transformer PT is connected to a connecting point of a Y-capacitor CY2 via a capacitor 50. By this, a high-frequency current is made to flow on the loop circuit which includes either the parasitic capacitors cp1, cp2 of the pulse transformer PT or the Y-capacitor CY2, and furthermore, the high-frequency current is prevented from flowing to the ground line GL. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes a power conversion circuit in which a series connection body of a pair of switching elements and a series connection body of a pair of capacitors are connected in parallel between a pair of wires insulated from a ground line, The present invention relates to a power conversion device in which the connection point of the capacitor is connected to the ground line.

  2. Description of the Related Art Known power conversion devices include a power conversion circuit (inverter) that includes a switching element that selectively connects a positive electrode and a negative electrode of a DC power supply to a terminal of an electric motor and is insulated from a ground line. The inverter or the like is required to be operated through an insulating means that insulates the low voltage system from the high voltage system because it is insulated from the low voltage system connected to the ground line. As this insulating means, it is also well known to use a pulse transformer.

  By the way, it is known that when the switching element of the inverter is operated at high speed, the voltage applied to the terminal of the motor fluctuates between the positive voltage and the negative voltage of the DC power supply, so that a high-frequency common mode current is generated. ing. The common mode current is generated by charging / discharging the parasitic capacitance between the originally insulated ground line and the inverter due to the voltage fluctuation due to the high-speed switching. When the common mode current flows through the ground line, the electronic device connected to the ground line may be damaged or electromagnetic radiation noise may be generated.

Therefore, conventionally, as seen in Patent Document 1 below, for example, it has been proposed to provide a pair of Y capacitors between a pair of power supply lines for supplying power to the motor. The Y capacitor is a series connection body of a pair of capacitors, and the connection point thereof is connected to the ground line. Thereby, it is possible to avoid the common mode current from flowing to another electronic device via the ground line.
JP 2000-315929 A

  By the way, the primary coil and the secondary coil of the pulse transformer have a parasitic capacitance. For this reason, in the case of driving the switching element using the pulse transformer, the parasitic capacitance between the primary side and the secondary side of the pulse transformer may become a flow path of the common mode current. However, since the Y capacitor is for a common mode countermeasure superimposed on a pair of wiring parts to which the Y capacitor is connected, the common mode current that flows through the parasitic capacitance of the pulse transformer depends on this. Is difficult to reduce.

  In addition to the above-mentioned pulse transformer, in a power converter provided with a transformer, the parasitic capacitance between the primary side and the secondary side becomes a flow path of the common mode current, so that high frequency noise is generated via the ground line. These facts that can cause various problems are generally common.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to connect a series connection body of a pair of switching elements and a pair of capacitors between a pair of wires insulated from a ground line. An object of the present invention is to provide a power conversion device that includes a power conversion circuit that is connected in parallel with a body and that can suitably suppress adverse effects due to the flow of high-frequency noise through a transformer.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  The invention according to claim 1 includes a power conversion circuit in which a series connection body of a pair of switching elements and a series connection body of a pair of capacitors are connected in parallel between a pair of wires insulated from a ground line. In the power conversion device in which the connection point of the pair of capacitors is connected to the ground line, a primary winding or a secondary winding is connected to the pair of wirings via the switching element. The transformer is characterized in that either one of the primary winding and the secondary winding of the transformer is connected to the connection point of the pair of capacitors.

  Although the primary side winding and the secondary side winding of the transformer are insulated, actually, the primary side winding and the secondary side winding are electrically coupled by a parasitic capacitance. For this reason, there exists a possibility that a high frequency current may flow between a primary side winding and a secondary side winding via the said parasitic capacitance. For this reason, when one of the primary side winding and the secondary side winding of the transformer is connected to the ground line, it flows between the primary side winding and the secondary side winding. High frequency current may flow to the ground line. In this regard, in the above-described invention, either one of the primary side winding and the secondary side winding of the transformer is connected to the connection point of the capacitor, thereby providing either the parasitic capacitance of the transformer or the pair of capacitors. A high-frequency current can flow on the loop circuit, and thus the flow of the high-frequency current to the ground line can be avoided. For this reason, the bad influence by the flow of the high frequency noise via a transformer can be controlled suitably.

  In addition, since the pair of capacitors is provided as a Y capacitor as a countermeasure against the common mode current flowing through the pair of wires, in order to make the flow path of the high-frequency current flowing through the transformer short-looped It is also possible to suppress the number of newly added electronic components as much as possible.

  According to a second aspect of the present invention, in the first aspect of the invention, the one of the windings of the transformer includes a midpoint tap, and the midpoint tap and a connection point of the pair of capacitors are connected. It is characterized by.

  When the impedance of the path including one of the pair of capacitors and the path including the other of the flow paths of the high-frequency current flowing through the transformer are different, mode conversion occurs and the common mode current is the normal mode current. Thus, the normal mode current becomes a common mode current. In order to avoid such mode conversion, it is desirable to match the impedances of the two paths. On the other hand, the power conversion circuit having the above configuration tends to have a symmetrical circuit configuration on the high-potential side wiring side and the low-potential side wiring side of the pair of wirings. In such a case, in order to make the impedances of the pair of paths equal, it is possible to avoid mode conversion by making the impedances of the parts inside the transformer of the pair of electrical paths the same. In the above invention, in view of this point, mode conversion can be suitably avoided by connecting the midpoint tap to the connection point of the pair of capacitors.

  The invention according to claim 3 is the invention according to claim 1 or 2, characterized in that any one of the windings of the transformer and a connection point of the pair of capacitors are connected via a capacitor. To do.

  The potential of the ground line can actually vary depending on the current flow mode. For this reason, the potential at the connection point of the pair of capacitors also varies depending on the current flow state of the ground line. For this reason, when either one of the windings is directly connected to the connection point of the pair of capacitors, the potential of any one of the windings may also vary depending on the current flow state of the ground line. There is. On the other hand, in the above invention, any one of the windings is connected to a connection point of the pair of capacitors via a capacitor, thereby suitably suppressing or avoiding a change in potential of the one of the windings. can do.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the transformer is a pulse transformer for driving the switching element, and one of the windings is It is a primary winding.

  In the case of the above invention, the secondary winding of the pulse transformer is connected to the pair of wiring sides so that it is insulated from the ground line, and the primary winding side is not insulated from the ground line. Become. However, a high-frequency current flowing from the secondary side to the primary side may flow to the ground line via the parasitic capacitance between the primary winding and the secondary winding of the pulse transformer. In this regard, in the above-described invention, a high-frequency current flows through a loop circuit including one of a pair of capacitors and a pulse transformer, thereby making a flow path of the high-frequency current into a short loop, and thus the high-frequency current flows out to the ground line. Can be avoided.

  When the invention according to claim 4 has the invention specific matter of claim 2 above, either one of the pair of capacitors and the pair of switching with respect to the connection point of the pair of capacitors and the midpoint tap. An electrical path that connects one of the elements and an electrical path that connects the other of the pair of capacitors and the other of the pair of switching elements are symmetrically connected. It is desirable to be characterized by being made.

  According to a fifth aspect of the present invention, the power conversion circuit according to the fourth aspect of the invention includes a transformer having a side to which the pair of switching elements are connected as one of a primary side and a secondary side. The other of the primary side and the secondary side is connected to the ground line.

  The primary side and the secondary side of the transformer included in the power conversion circuit are electrically coupled by a parasitic capacitance. For this reason, a high-frequency current may flow through a loop circuit constituted by any one of the above, the ground line, the primary side of the pulse transformer, and the secondary side of the pulse transformer. In this regard, in the above-described invention, by configuring a circuit that is shorter than the loop circuit, it is possible to avoid a high-frequency current from flowing through the loop circuit including the ground line.

  The invention according to claim 6 is the invention according to any one of claims 1 to 3, wherein the transformer is a transformer included in the power conversion circuit, and one of the windings is the The winding is connected to a pair of switching elements, and one of the other windings is connected to the ground line.

  The primary side and the secondary side of the transformer included in the power conversion circuit are electrically coupled by a parasitic capacitance. For this reason, a high-frequency current may flow through a loop circuit constituted by any one of the other, the ground line, the connection point of the pair of capacitors, and the pair of capacitors. In this regard, in the above-described invention, by configuring a circuit that is shorter than the loop circuit, it is possible to avoid a high-frequency current from flowing through the loop circuit including the ground line.

  In the case where the invention according to claim 6 includes the invention specific matter according to claim 2, one of the pair of capacitors and the middle of the connection path of the pair of capacitors and the midpoint tap. It is desirable that the electrical path between the point taps and the other one of the pair of capacitors and the electrical path between the midpoint taps are electrically connected so as to have symmetry.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the pair of wirings constitute an in-vehicle high voltage system insulated from the in-vehicle low voltage system.

  The in-vehicle high voltage system is insulated from a ground line connected to the vehicle body. However, when the power conversion device includes a transformer, a high-frequency current may flow from the high-voltage system side to the low-voltage system side via a parasitic capacitance between the primary side and the secondary side of the transformer. For this reason, the utility value of invention of Claims 1-6 is especially high.

(First embodiment)
Hereinafter, a first embodiment in which a power conversion device according to the present invention is applied to a power conversion device mounted on a hybrid vehicle will be described with reference to the drawings.

  FIG. 1 shows an overall configuration of a system according to the present embodiment.

  The illustrated high voltage battery 10 is a power source of an electric motor (not shown) as an in-vehicle power generation device, and outputs a predetermined high voltage (several hundred volts). The DCDC converter CV steps down the voltage of the high voltage battery 10 and outputs it. Specifically, the DCDC converter CV is an insulating converter including the transformer 20. One terminal of the primary side coil 20a of the transformer 20 can be electrically connected to the positive electrode side of the high-voltage battery 10 via the high-potential side switching element Sw1 and the high-potential side wiring Lp. It can be electrically connected to the negative electrode side of the high-voltage battery 10 via the element Sw2 and the low-potential side wiring Ln. Further, the other terminal of the primary side coil 20a of the transformer 20 can be electrically connected to the positive electrode side of the high voltage battery 10 via the high potential side switching element Sw3 and the high potential side wiring Lp. It can be electrically connected to the negative electrode side of the high voltage battery 10 via the element Sw4 and the low potential side wiring Ln. Here, in the present embodiment, N-channel MOS transistors are illustrated as the switching elements Sw1 to Sw4. These switching elements Sw1 to Sw4 have the same specifications (same characteristics, same dimensions, same rated current, etc.). Free wheel diodes D1 to D4 are connected between the input / output terminals of the switching elements Sw1 to Sw4, respectively.

  According to such a configuration, the high potential side switching element Sw1 and the low potential side switching element Sw4 are turned on, and the low potential side switching element Sw2 and the high potential side switching element Sw3 are turned on. The voltage polarity of the primary side coil 20a is inverted, and consequently the voltage polarity of the secondary side coil 20b is also inverted. Regardless of the reversal of the voltage polarity of the secondary coil 20b, a pair of terminals of the secondary coil 20b are connected to the anode sides of the diodes RD1 and RD2, respectively, in order to apply a constant voltage. The cathode sides of these diodes RD 1 and RD 2 are short-circuited and output to the smoothing circuit 22. In this embodiment, as the smoothing circuit 22, an LC filter including a coil 22a and a capacitor 22b is illustrated.

  The primary side of the high voltage battery 10 and the DCDC converter CV constitutes an in-vehicle high voltage system and is insulated from the ground line GL. On the other hand, the secondary side of the DCDC converter CV constitutes an in-vehicle low-pressure system that operates based on the ground line GL connected to the vehicle body. In order to achieve such a setting, in this embodiment, the midpoint tap mt of the secondary coil 20b of the transformer 20 is connected to the ground line GL. As a result, the diodes RD1 and RD2 have the high potential side switching element Sw1 and the low potential side switching element Sw4 turned on or the low potential side switching element Sw2 and the high potential side switching element Sw3 turned on. Accordingly, a voltage of “½” of the voltage across the secondary coil 20b is alternately output. The midpoint tap mt is a terminal connected to the center of the transformer coil (a midpoint that is equidistant from both terminals).

  The output voltage of the DCDC converter CV is applied to the low voltage battery 12. The low voltage battery 12 is a power supply means for an electric load in the in-vehicle low voltage system. FIG. 1 illustrates a load 24, an auxiliary power supply 26, and a control device 30 as such an electric load. Here, examples of the load 24 include an air conditioner and a headlight. Further, the auxiliary power source 26 is for stepping down the voltage (for example, “12V”) of the low-voltage battery 12 to generate a predetermined stable voltage.

  On the other hand, the control device 30 is control means that uses the low-voltage battery 12 as a control target and uses the auxiliary power supply 26 as a direct power supply. Specifically, the high potential side switching elements Sw1 and Sw3 and the low potential side switching elements Sw2 and Sw4 of the DCDC converter CV are operated in order to control the state of charge (SOC) of the low voltage battery 12 as desired. Specifically, the high potential side switching elements Sw1 and Sw3 and the low potential side switching elements Sw2 and Sw4 are operated via the drive circuit DC.

  FIG. 1 illustrates the internal circuit of the drive circuit DC of the high potential side switching element Sw1 and the low potential side switching element Sw2. As shown in the figure, the drive circuit DC includes a pulse transformer PT. The secondary coil of the pulse transformer PT is a pair of coils including a coil connected between the drain and gate of the high potential side switching element Sw1 and a coil connected between the drain and gate of the low potential side switching element Sw2. Configured. On the other hand, mutually inverted voltages are applied to the pair of terminals of the primary coil of the pulse transformer. Thus, voltages that are logically inverted from each other are applied between the drain and gate of the high potential side switching element Sw1 and between the drain and gate of the low potential side switching element Sw2. The configuration of the drive circuit DC of the high potential side switching element Sw3 and the low potential side switching element Sw4 is the same.

  The DCDC converter CV includes a capacitor 42 between the high potential side wiring Lp and the low potential side wiring Ln for suppressing fluctuations in the input voltage. Further, the DCDC converter CV includes the following as a countermeasure by superimposing the common mode current on the high potential side wiring Lp and the low potential side wiring Ln. First, Y capacitors CY1 and CY2 are provided between the high potential side wiring Lp and the low potential side wiring Ln. These Y capacitors CY1 and CY2 are a series connection body of a pair of capacitors, and the connection point thereof is connected to the ground line GL. Further, the high-potential side Y capacitor CY1 (CY2) and the low-potential side Y capacitor CY1 (CY2) have the same specifications (same capacity, same dimensions, etc., particularly the same impedance). A common mode choke coil 40 is provided between the Y capacitors CY1 and CY2.

  According to such a configuration, it is possible to avoid the common mode current superimposed on the high potential side wiring Lp and the low potential side wiring Ln from adversely affecting the control device 30, the load 24, and the like via the ground line GL.

  Incidentally, parasitic capacitors cp1 and cp2 are usually interposed between the primary side coil and the secondary side coil of the pulse transformer PT. A parasitic capacitor cp3 is also interposed between the primary side coil 20a and the secondary side coil 20b of the transformer 20 of the DCDC converter CV. For this reason, there is a possibility that a common mode current flows through an electric path including the parasitic capacitors cp1 and cp3 and the ground line GL and an electric path including the parasitic capacitors cp2 and cp3 and the ground line GL. In this case, there is a possibility that an electric load between them and connected to the ground line GL may be adversely affected.

  Therefore, in the present embodiment, the midpoint tap mt of the primary transformer of the pulse transformer PT and the connection point of the Y capacitor CY2 are connected via the capacitor 50. As a result, for example, when high-frequency noise generated on the primary side of the DCDC converter CV is superimposed on the low-voltage system side via the parasitic capacitor cp1, as shown by a dotted line in FIG. A short loop can be formed in the loop circuit of the tap mt, the capacitor 50, the Y capacitor CY2 on the high potential side, the high potential side wiring Lp, and the high potential side switching element Sw1. On the other hand, when the midpoint tap mt of the primary transformer of the pulse transformer PT is not connected to the connection point of the Y capacitor CY2, as shown by a dotted line in FIG. 3, the parasitic capacitor cp1, the control device 30, A common mode current flows through a loop circuit including the ground line GL, the parasitic capacitor cp3, and the secondary coil of the pulse transformer PT. As a result, the control device 30 may be adversely affected. In the figure, the load 24 is not included in the loop circuit. However, since the actual connection point between the load 24 and the ground line GL is arbitrary, the load 24 may be adversely affected.

  As described above, in the present embodiment, the midpoint tap mt of the secondary coil is connected to the connection point of the Y capacitor CY2. This is because the impedance of the loop circuit including the midpoint tap mt, the capacitor 50, the high potential side Y capacitor CY2, the high potential side wiring Lp, and the high potential side switching element Sw1 (Sw3), the midpoint tap mt, and the capacitor 50. This is a setting for equalizing the impedance of the loop circuit including the low-potential-side Y capacitor CY2, the low-potential-side wiring Ln, and the low-potential-side switching element Sw2 (Sw4). This is because the electrical path of the primary side coil of the high potential side Y capacitor CY2, the high potential side wiring Lp, the high potential side switching element Sw1 (Sw3), and the pulse transformer PT, the low potential side Y capacitor CY2, It is assumed that the electrical path of the potential side wiring Ln, the low potential side switching element Sw2 (Sw4), and the primary side coil of the pulse transformer PT has geometric symmetry. That is, in this case, since the impedance of the pair of electric paths is considered to be equal, the impedance of the pair of loop circuits can be equalized by connecting the connection point of the Y capacitor CY2 and the midpoint tap mt. . Thus, by making the impedances of the pair of loop circuits equal, it is possible to avoid mode conversion in which common mode noise is converted into normal mode noise or normal mode noise is converted into common mode noise.

  Incidentally, the high-frequency current is prevented from flowing through the electrical path shown in FIG. 3, and the high-frequency current flows through the loop circuit shown in FIG. 2 in FIG. 2, compared to the electrical path shown in FIG. This is because the loop circuit shown has a smaller impedance. This is realized because of the short loop. That is, since the electrical resistance of the wiring is proportional to the wiring length, the impedance is reduced by a short loop compared to the path passing through the ground line GL.

  Note that the connection point of the Y capacitor CY2 and the midpoint tap mt are connected via the capacitor 50 to prevent the potential of the primary transformer of the pulse transformer PT from fluctuating due to the potential fluctuation of the ground line GL. Is to do. That is, when a current flows through the ground line GL, the potential of the ground line GL varies depending on the location. When the ground line GL and the midpoint tap mt are connected without passing through the capacitor 50, the influence of the fluctuation of the potential at the connection point of the ground line GL with the Y capacitor CY2 is affected by the midpoint tap mt. Will occur directly. On the other hand, when the connection is made via the capacitor 50, it is possible to avoid the influence of the low frequency fluctuation such as the fluctuation of the current flowing through the ground line GL from occurring in the midpoint tap mt.

  According to the embodiment described above, the following effects can be obtained.

  (1) The primary winding of the pulse transformer PT was connected to the connection point of the Y capacitor CY2. As a result, the high-frequency current can flow on the loop circuit including any one of the parasitic capacitors cp1 and cp2 and the Y capacitor CY2 of the pulse transformer PT. As a result, the high-frequency current flows to the ground line GL. It can be avoided. In addition, since the Y capacitor CY2 is provided as a countermeasure against the common mode current flowing through the high potential side wiring Lp and the low potential side wiring Ln, the flow path of the high frequency current flowing through the pulse transformer PT is made into a short loop. Therefore, it is possible to suppress the number of newly added electronic components as much as possible.

  (2) The midpoint tap mt and the connection point of the Y capacitor CY2 are connected. Thereby, mode conversion can be avoided suitably.

  (3) The midpoint tap mt and the connection point of the Y capacitor CY2 are connected via the capacitor 50. Thereby, the fluctuation | variation of the electric potential of the midpoint tap mt can be suppressed or avoided suitably.

  (4) The DCDC converter CV is configured to include the transformer 20. In this case, the primary side coil 20a and the secondary side coil 20b of the transformer 20 are electrically coupled by the parasitic capacitor cp3. For this reason, a loop circuit including a ground line GL is formed together with parasitic capacitors cp1 and cp2 that electrically couple the primary coil and the secondary coil of the pulse transformer PT. For this reason, it is a configuration in which measures against high-frequency current flowing through the primary side and the secondary side of the pulse transformer PT are particularly desired.

  (5) The in-vehicle high voltage system insulated from the in-vehicle low voltage system is configured by the primary side of the DCDC converter CV. As a result, high-frequency current flows from the high-voltage system side to the low-voltage system side via the parasitic capacitors cp1 and cp2 between the primary side and the secondary side of the pulse transformer and the parasitic capacitor cp3 between the primary side and the secondary side of the transformer 20. May flow. For this reason, it is a configuration in which measures against high-frequency current flowing through the primary side and the secondary side of the pulse transformer PT are particularly desired.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 4 shows a system configuration according to the present embodiment. In FIG. 4, members corresponding to those shown in FIG. 1 are given the same reference numerals for the sake of convenience.

  As illustrated, in this embodiment, the midpoint tap mt of the primary side coil 20a of the transformer 20 is connected to the connection point of the Y capacitor CY2 via the capacitor 60. Accordingly, it is possible to avoid the common mode current from flowing through the parasitic capacitor cp3 between the primary side coil 20a and the secondary side coil 20b of the transformer 20, as indicated by a dotted line in FIG. That is, instead of the electrical path including the ground line GL, the midpoint tap mt of the primary coil 20a, the capacitor 60, the high potential side Y capacitor CY2, the high potential side wiring Lp, and the high potential side switching element Sw3 (Sw1) The high frequency current flows through the loop circuit including This is because the impedance of the loop circuit including the midpoint tap mt of the primary side coil 20a, the capacitor 60, the Y capacitor CY2 on the high potential side, the high potential side wiring Lp, and the high potential side switching element Sw3 (Sw1) is This is because the impedance is lower than the impedance of the electrical path indicated by the dotted line in FIG. In order to realize such setting, in this embodiment, the distance between the connection point of the Y capacitor CY2 and the connection point between the ground lines GL and the connection point between the midpoint tap mt of the secondary coil 20b and the ground line GL is set. We try to keep them apart as much as possible.

  In this embodiment, the reason for connecting the connection point of the Y capacitor CY2 and the midpoint tap mt of the primary coil 20a is that the midpoint tap mt of the primary side coil 20a, the capacitor 60, the Y on the high potential side. Loop circuit including capacitor CY2, high potential side wiring Lp, and high potential side switching element Sw1 (Sw3), midpoint tap mt of primary side coil 20a, capacitor 60, low potential side Y capacitor CY2, low potential side The purpose is to equalize the impedance of the loop circuit including the wiring Ln and the low-potential side switching element Sw2 (Sw4). This is because an electric path including a high-potential-side Y capacitor CY2, a high-potential-side wiring Lp, and a high-potential-side switching element Sw1 (Sw3), a low-potential-side Y capacitor CY2, a low-potential-side wiring Ln, and a low-potential It is assumed that the electrical path including the side switching element Sw2 (Sw4) has geometric symmetry.

  According to the present embodiment described above, the following effects can be obtained in addition to the effects according to the above-described effects (2) to (5) of the first embodiment.

  (6) The midpoint tap mt of the primary side coil 20a of the transformer 20 is connected to the connection point of the Y capacitor CY2. Thereby, it is possible to avoid the common mode current from flowing to the ground line GL via the parasitic capacitor cp3 between the primary side coil 20a and the secondary side coil 20b of the transformer 20.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  -The characteristic part of 2nd Embodiment may be further added to the said 1st Embodiment.

  In the first embodiment, the midpoint tap mt of the primary coil of the pulse transformer PT is connected to the Y capacitor CY2 side, but may be connected to the Y capacitor CY1 side. However, the impedance of the loop circuit including the midpoint tap mt, the connection point of the Y capacitor CY1, the wiring Lp (or the wiring Ln), and the parasitic capacitor cp1 (parasitic capacitor cp2) is greater than the parasitic capacitor cp1 (parasitic capacitor cp2) and The impedance is made smaller than the impedance of the loop circuit (FIG. 3) including the ground line GL.

  In the first embodiment, with respect to the capacitor 50, a loop circuit including a high-potential side Y capacitor CY2 and a high-potential side switching element Sw1 (high-potential side switching element Sw3), and a low-potential side Y capacitor CY2 In addition, the configuration in which the impedance of the loop circuit including the low potential side switching element Sw2 (low potential side switching element Sw4) is made substantially equal is not limited to a configuration in which these loop circuits are geometrically symmetric. For example, even if the configuration is geometrically asymmetric, the impedance of both loop circuits can be made substantially equal by connecting an adjusting resistor to one of them. Further, for example, when the impedances of portions other than the pulse transformer PT in the pair of loop circuits are different from each other, instead of connecting the primary side coil of the pulse transformer PT to the capacitor 50 at the midpoint tap mt, By connecting to the capacitor 50 at a position (tap) shifted from the center of the primary side coil, the impedance shift of the pair of loop circuits may be compensated.

  In the first embodiment, the power conversion circuit is not limited to the DCDC converter CV. For example, it may be a DCDC converter found in Japanese Patent Application Laid-Open No. 2005-51994. Further, the DCDC converter is not limited to a step-down converter, and may be a step-up converter. Furthermore, not only a DCDC converter, but also a three-phase inverter that selectively electrically connects each phase of the three-phase motor to either the positive electrode or the negative electrode of the DC power supply. Even in such a case, the application of the present invention is effective as a countermeasure against high-frequency current through a pulse transformer that drives the switching elements provided therein.

  In the second embodiment, the midpoint tap mt of the primary side coil 20a of the transformer 20 is connected to the Y capacitor CY2 side, but may be connected to the Y capacitor CY1 side. However, the impedance of the loop circuit including the midpoint tap of the primary side coil 20a of the transformer 20 and the capacitor 60, the Y capacitor CY1, and the high potential side wiring Lp (or the low potential side wiring Ln) is greater than that of the ground line GL and the transformer. It is made to become lower than the impedance of the loop circuit (FIG. 5) provided with 20.

  In the second embodiment, with respect to the capacitor 60, as a configuration in which the impedances of the loop circuit including the high-potential side Y capacitor CY2 and the loop circuit including the low-potential side Y capacitor CY2 are substantially equal, The loop circuit is not limited to a configuration that is geometrically substantially symmetrical. For example, even if the configuration is geometrically asymmetric, the impedance of both loop circuits can be made substantially equal by connecting an adjusting resistor to one of them. Further, for example, when the impedances of portions other than the transformer 20 in the pair of loop circuits are different from each other, the primary side coil of the transformer 20 is replaced with the primary 60 instead of being connected to the capacitor 60 by the midpoint tap mt. By connecting to the capacitor 60 at a position (tap) shifted from the center of the side coil, the impedance deviation of the pair of loop circuits may be compensated.

  The impedance of the loop circuit including the midpoint tap of the primary side coil 20a of the transformer 20 and the capacitor 60, the Y capacitor CY2, and the high potential side wiring Lp (or the low potential side wiring Ln) is the ground line GL and the transformer 20 The technique for making the impedance lower than the impedance of the loop circuit including the above is not limited to the one exemplified in the second embodiment. For example, by connecting a resistor between the midpoint tap mt and the ground line GL of the primary side coil 20a of the transformer 20 or between the midpoint tap mt and the ground line GL of the secondary side coil 20b, the above setting is performed. It may be realized.

  The high-potential side wiring Lp and the low-potential side wiring Ln and the ground line GL are not limited to those constituting the high-voltage system and the low-pressure system of the hybrid vehicle. For example, you may comprise each of the high voltage | pressure system and low voltage | pressure system of an electric vehicle.

1 is a system configuration diagram according to a first embodiment. FIG. The circuit diagram which shows the effect of the embodiment. The circuit diagram which shows the common mode noise in the conventional circuit. The system block diagram concerning 2nd Embodiment. The circuit diagram which shows the common mode noise in the conventional circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... High voltage battery, 12 ... Low voltage battery, 20 ... Transformer, 24 ... Load, 30 ... Control apparatus, CV ... DCDC converter (one embodiment of a power converter circuit), CY1, CY2 ... Y capacitor, mt ... Midpoint tap, Lp: High potential side wiring, Ln: Low potential side wiring, GL: Ground line.

Claims (7)

A power conversion circuit is provided in which a series connection body of a pair of switching elements and a series connection body of a pair of capacitors are connected in parallel between a pair of wires insulated from a ground line, and the connection of the pair of capacitors In a power conversion device in which a point is connected to the ground line,
A transformer in which a primary winding or a secondary winding is connected to the pair of wirings via the switching element;
One of the primary side winding and the secondary side winding of this transformer, and the connection point of said pair of capacitor | condenser were connected, The power converter device characterized by the above-mentioned. One of the windings of the transformer includes a midpoint tap,
The power converter according to claim 1, wherein the midpoint tap and a connection point of the pair of capacitors are connected.   The power converter according to claim 1 or 2, wherein one of the windings of the transformer and a connection point of the pair of capacitors are connected via a capacitor.   4. The transformer according to claim 1, wherein the transformer is a pulse transformer that drives the switching element, and the one of the windings is a primary winding. Power converter. The power conversion circuit includes a transformer having a side to which the pair of switching elements are connected as one of a primary side and a secondary side,
The power converter according to claim 4, wherein one of the primary side and the secondary side is connected to the ground line.   The transformer is a transformer included in the power conversion circuit, and one of the windings is a winding connected to the pair of switching elements, and the other winding is the ground line. The power conversion device according to claim 1, wherein the power conversion device is connected to the power conversion device.   The power converter according to any one of claims 1 to 6, wherein the pair of wirings constitute an in-vehicle high-voltage system insulated from the in-vehicle low-voltage system.

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