JP2009273272A - Inverter module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter module that suppresses generation of a common-mode current. <P>SOLUTION: The inverter module includes a switching element TR and a diode D anti-parallel-connected to the switching element TR as one arm, and an arm series connector including two arms as an upper arm and a lower arm so as to connect the two arms in series. The inverter module is provided with a cooling device 28 for cooling the switching element TR and the diode D, and an insulating substrate 22 interposed between the switching element TR/diode D and the cooling device 28. The inverter module is also configured such that a capacitor, which is constituted between the switching element TR/diode D and the cooling device 28 respectively included in the upper arm, is smaller than a capacitor constituted between the switching element TR/diode D and the cooling device 28 respectively included in the lower arm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inverter module used in an inverter circuit.

  In the inverter module of the power converter, a common mode voltage is generated between the inverter and a load (usually a motor). This common mode voltage may cause a common mode current to flow, causing problems such as radiation noise.

  In Patent Document 1, in a package including a series circuit of switching arms, a copper base for cooling is arranged outside the package, and the upper arm is mounted over the area of the copper base on which the lower arm in the series circuit of switching arms is mounted. A technique for reducing the generation of common mode current by increasing the area of the copper base to be produced is disclosed.

  In Patent Document 2, a common mode choke coil is connected between an inverter and an electric device, and a series connection body of a capacitor and a resistor is connected to a wiring between the choke coil and the electric device. A technique for reducing the generation of common mode current by connecting a series connection in common and connecting it to a virtual grounding portion having the same potential as the ground for a frequency higher than that of the power supply is disclosed.

  Patent Document 3 discloses a control device in which a noise filter provided on the input side of an inverter circuit is grounded via a housing of the device, and is provided between a capacitor connected to an AC line and the capacitor. Disclosed is a technique for reducing the generation of common mode current by including a coil, a clamper provided between a connection point between the capacitor and the housing, and a capacitor connected in parallel to the clamper. ing.

JP 2007-181351 A JP 2001-69762 A JP 2003-143753 A

  In the technique of providing a filter including a choke coil or the like in the above prior art, a large current of several hundred A may flow between the inverter and the load (motor or the like), and a huge coil is used to prevent magnetic saturation of the inductance. It is necessary to use it. Accordingly, there is a problem that downsizing of the inverter module is hindered.

  In addition, the technique of providing an electromagnetic shield to prevent magnetic noise due to common mode current from leaking to the outside increases the manufacturing cost of the device and does not eliminate the noise source, so there is a problem that it is not a fundamental measure. .

  One aspect of the present invention is an arm series connection body in which a switching element and a diode connected in reverse parallel to the switching element are used as one arm, and two arms are connected in series as an upper arm and a lower arm, respectively. A modular inverter module, wherein each arm includes a cooling device for cooling the switching element and the diode, and an insulating substrate sandwiched between the switching element, the diode and the cooling device, A capacitor between the switching element and the diode included in the upper arm and the cooling device is smaller than a capacitor between the switching element and the diode and the cooling device included in the lower arm. It is an inverter module.

  Here, the capacitor between the switching element and the diode included in the lower arm and the cooling device is 33 times the capacitor between the switching element and the diode and the cooling device included in the upper arm. The above is preferable.

  In addition, it is preferable that the thickness of the insulating substrate included in the upper arm is 100 times or more the thickness of the insulating substrate included in the lower arm.

  It is also preferable that an external capacitor is connected between the switching element and the diode included in the lower arm and the cooling device.

  That is, an inverter module includes a capacitor between the switching element and the diode included in the upper arm and the cooling device, and a capacitor between the switching element and the diode and the cooling device included in the lower arm. It is preferable that the load case connected to the inverter and the inverter module case have the same potential.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the common mode electric current in an inverter module can be suppressed. Thereby, electromagnetic noise can be reduced.

  FIG. 1 is a diagram showing a basic inverter circuit 100. The inverter circuit 100 is connected between a power source 200 and a load (motor) 300. The inverter circuit 100 includes a rectifier module 10 including six diodes D1 to D6, a capacitor 12, an inverter module 14 including power switching elements TR1 to TR6 and diodes D7 to D12.

  The rectifier module 10 is configured by connecting in parallel three series-connected bodies in which two diodes D1 to D6 are connected in series. The rectifier module 10 is connected in parallel with the capacitor 12 and the inverter module 14. Further, each phase of the power source 200 is applied between two diodes included in the three series-connected bodies.

  The inverter module 14 includes six arms in which diodes D7 to D12 are connected in antiparallel to each of the switching elements TR1 to TR6. The switching elements TR1 to TR6 are high power switching elements such as insulated gate bipolar transistors (IGBTs) and field effect transistors (MOSFETs), for example. The diodes D7 to D12 are, for example, large-capacity PIN diodes. The six arms are two series-connected bodies connected in series as two upper arms and two lower arms, and three series-connected bodies are connected in parallel to constitute the inverter module 14. Each phase of the load 300 is connected between two arms included in three series-connected bodies.

  Each arm includes a switching element TR (TR1 to TR6), a diode D (D7 to D12), a first electrode 20, an insulating substrate 22, and a second electrode 24, as shown in the perspective view of FIG. 2 and the side view of FIG. The solder material 26 and the cooling device 28 are included.

  The high voltage side terminal (the collector of the N channel IGBT, the drain of the N channel MOSFET, etc.) of the switching element TR is connected to the first electrode 20 by the solder material 26. The high-voltage side terminal of the diode D (such as the cathode of the PIN diode) is also connected to the first electrode 20. The first electrode 20 is bonded to the surface of the insulating substrate 22, and the back surface of the insulating substrate 22 is bonded to the second electrode 24. Further, the second electrode 24 is bonded to the cooling device 28 by the solder material 26 while being electrically connected.

  With such a configuration, a capacitor is generated between the first electrode 20 and the second electrode 24 by the insulating substrate 22 sandwiched between the first electrode 20 and the second electrode 24. Therefore, the equivalent circuit of each arm is such that the capacitor C is connected to the connection side of the high voltage side terminal of the switching element TR and the high voltage side terminal of the diode D, as shown in FIG.

  In the present embodiment, each arm is configured such that the capacitor CU generated in the upper arm is smaller than the capacitor CL generated in the lower arm. For example, when the insulating substrate 22 used for the upper arm and the lower arm is made of the same material, the insulating substrate 22 constituting the upper arm is made thicker than the insulating substrate 22 constituting the lower arm. In addition, the dielectric constant of the insulating substrate 22 constituting the upper arm is made smaller than the dielectric constant of the insulating substrate 22 constituting the lower arm.

  FIG. 5 is a diagram showing an equivalent circuit when the inverter module 14 is applied to the inverter circuit 100. Here, the parasitic inductance in the inverter module 14 is ignored.

  A bridge circuit including an inductance Lc of a cable connecting the inverter module and the load (motor), a capacitor CM between the load (motor) and the case, and capacitors CU and CL generated in the inverter module is configured. . By this bridge circuit, electrical balance is achieved, the potential of the load (motor) case and the potential of the inverter module case are kept substantially constant, and between the load (motor) and the inverter via a vehicle or the like. The common mode current flowing through can be suppressed.

  The operation mode of the inverter is divided into two types: (1) upper arm 1 phase and lower arm 2 phase are conductive, and (2) upper arm 2 phase and lower arm 1 phase are conductive. Thus, these two states are repeated.

  Considering the equivalent circuit of the entire system shown in FIG. 5 and the operation mode of the inverter shown in FIG. 6, two paths are generated from the high voltage side to the low voltage side of the inverter. That is, as shown in FIG. 7, the first path is a conductive upper arm → parasitic inductor Lc of the cable to the motor → parasitic capacitor CM between the motor winding and the motor case → motor case → motor case and motor winding. Between the parasitic capacitor CM between the cable and the parasitic inductor Lc of the cable to the motor → the lower arm conducting. As shown in FIG. 8, the second path is a conductive upper arm → a parasitic capacitor CL of the lower arm paired with the conductive upper arm → a case of the cooling device 28 → a parasitic capacitor CL of the conductive lower arm → conductive. Either a path of a lower arm or a path of a parasitic capacitor CU of an upper arm that is not conductive → a case of the cooling device 28 → a parasitic capacitor CL of a lower arm that is conductive → a lower arm that is conductive.

  FIG. 9 is a diagram in which these two paths are rewritten as a bridge circuit with a parasitic inductor LG between the case of the cooling device 28 and the motor case serving as a common mode current path. FIG. 9A is an equivalent circuit when the upper arm 1 phase and the lower arm 2 phase are conductive, and FIG. 9B is an equivalent circuit when the upper arm 2 phase and the lower arm 1 phase are conductive.

FIG. 10 is a diagram showing these circuits in a simplified manner. In this circuit, when the formula (1) holds, the common mode current does not flow.
Za: Zb = Zc: Zd (1)

  In either state of FIGS. 9A and 9B, the condition for satisfying Equation (1) is that the parasitic capacitor CL of the lower arm is sufficiently larger than the parasitic capacitor CU of the upper arm. That is, the common mode current stops flowing when the lower arm parasitic capacitor CL >> the upper arm parasitic capacitor CU is established.

  The operation of this embodiment was confirmed using circuit simulation. The simulation was performed with the circuit configuration of FIG. FIG. 12 shows the result of the simulation. In this simulation, the voltage of each phase of the inverter has a peak value of 217 V, a cycle of 200 μsec (duty 50%), and a pulse rise and fall time of 50 nsec.

  When the parasitic capacitor CU of the upper arm was 0, the common mode current flowing through the parasitic inductor LG was very small. Further, when the upper arm parasitic capacitor CU is increased, the ratio of the current flowing through the lower arm parasitic capacitor CL to the current flowing through the parasitic inductor LG is substantially proportional to the ratio of the parasitic capacitor CL and the parasitic capacitor CU × 3. I understood.

  The ratio CL / CU between the parasitic capacitor CL of the lower arm and the capacitor CU (= 3CU) formed by parallel connection of the parasitic capacitors CU of the three upper arms is 100 or more, that is, the parasitic capacitor CL of the lower arm and the upper arm If the ratio CL / CU with respect to the parasitic of the parasitic capacitor CU is 33 or more, a high noise reduction effect can be obtained.

  For example, it is preferable to make the thickness of the insulating substrate 22 constituting the upper arm 100 times or more larger than the thickness of the insulating substrate 22 constituting the lower arm. For example, in the case where the insulating substrate 22 constituting the upper arm is made of aluminum nitride (AlN) or alumina (Al2O3) to be 0.5 mm or more and 5 mm or less, in order to constitute such a lower arm, the insulating substrate 22 may be a DLC (Diamond). It is preferable that the thickness is 0.005 mm or more and 0.05 mm or less using Like Carbon or silicon nitride (SiN).

  As shown in FIG. 13, in the configuration of FIG. 3, an external capacitor Cext may be connected between the first electrode 20 and the second electrode 24 of the lower arm to adjust the capacitor. FIG. 14 is a diagram showing an equivalent circuit when the external capacitor Cext is connected as shown in FIG. Thus, by connecting the external capacitor Cext, the parasitic capacitor CL of the lower arm can be made sufficiently larger than the parasitic capacitor CU of the upper arm. For example, when the insulating substrate 22 of the upper arm and the lower arm are made of the same material and the same thickness, the capacitor CL formed between the first electrode 20 and the second electrode 24 of the lower arm becomes the first electrode 20 of the upper arm. And the capacitor CU formed between the second electrode 24 and the second electrode 24.

It is a figure which shows the basic composition of the inverter circuit in embodiment of this invention. It is a perspective view which shows the structure of the inverter module in embodiment of this invention. It is a side view which shows the structure of the inverter module in embodiment of this invention. It is a figure which shows the equivalent circuit of the inverter module in embodiment of this invention. It is a figure which shows the equivalent circuit of the inverter circuit in embodiment of this invention. It is a figure which shows the operation mode of the inverter circuit in embodiment of this invention. It is a figure which shows the current pathway in the 1st operation mode of the inverter circuit in embodiment of this invention. It is a figure which shows the electric current path in the 2nd operation mode of the inverter circuit in embodiment of this invention. It is a figure which shows the equivalent circuit in each operation mode of the inverter circuit in embodiment of this invention. It is a figure which shows the bridge circuit with respect to the common mode current of the inverter circuit in embodiment of this invention. It is a figure which shows the equivalent circuit for the simulation of the inverter circuit in embodiment of this invention. It is a figure which shows the simulation result of the inverter circuit in embodiment of this invention. It is a side view which shows the structure of the inverter module in the modification of this invention. It is a figure which shows the equivalent circuit of the inverter module in the modification of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Rectifier module, 12 Capacitor, 14 Inverter module, 20 1st electrode, 22 Insulating board, 24 2nd electrode, 26 Solder material, 28 Cooling device, 100 Inverter circuit, 200 Power supply, 300 Load (motor).

Claims (5)

An inverter module in which a switching element and a diode connected in reverse parallel to the switching element are used as one arm, and an arm series connection body in which two arms are connected in series as an upper arm and a lower arm, respectively, is modularized. ,
Each arm includes a cooling device for cooling the switching element and the diode, and an insulating substrate sandwiched between the switching element and the diode and the cooling device,
A capacitor between the switching element and the diode included in the upper arm and the cooling device is smaller than a capacitor between the switching element and the diode and the cooling device included in the lower arm. Inverter module. The inverter module according to claim 1,
The capacitor between the switching element and the diode included in the lower arm and the cooling device is 33 times or more of the capacitor between the switching element and the diode and the cooling device included in the upper arm. An inverter module characterized by that. The inverter module according to claim 1 or 2,
An inverter module, wherein a thickness of the insulating substrate included in the upper arm is 100 times or more a thickness of the insulating substrate included in the lower arm. The inverter module according to claim 1 or 2,
An inverter module, wherein an external capacitor is connected between the switching element and the diode included in the lower arm and the cooling device. The inverter module according to any one of claims 1 to 4,
The capacitor between the switching element and the diode included in the upper arm and the cooling device and the capacitor between the switching element and the diode and the cooling device included in the lower arm are connected to an inverter module. An inverter module characterized in that a load case and an inverter module case have the same potential.

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