Patent Publication Number: US-2022231617-A1

Title: Electric power conversion apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Application No. PCT/JP2020/031255 filed on Aug. 19, 2020, which is based on and claims priority from Japanese Patent Application No. 2019-182844 filed on Oct. 3, 2019. The entire contents of these applications are incorporated by reference into the present application. 
    
    
     BACKGROUND 
     1 Technical Field 
     The present disclosure relates to electric power conversion apparatuses. 
     2 Description of Related Art 
     Vehicles, such as electric vehicles and hybrid vehicles, are generally equipped with electric power conversion apparatuses that perform electric power conversion between DC power and AC power. 
     SUMMARY 
     According to the present disclosure, there is provided an electric power conversion apparatus which includes a semiconductor module, a control circuit board and a wireless communication unit. The semiconductor module has at least one semiconductor element built therein. The control circuit board is configured to control the semiconductor module. The wireless communication unit is configured to wirelessly communicate electrical signals between the semiconductor module and the control circuit board. The wireless communication unit includes a first communication device provided on the control circuit board so as to face the semiconductor module, and a second communication device provided on the semiconductor module so as to face the control circuit board. Moreover, there are no obstacles on a straight path between the first and second communication devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an electric power conversion apparatus according to a first embodiment. 
         FIG. 2  is a cross-sectional view taken along the line II-II and viewed along arrows in  FIG. 1 . 
         FIG. 3  is a circuit diagram illustrating an inverter circuit of the electric power conversion apparatus according to the first embodiment. 
         FIG. 4  is a schematic diagram illustrating a wireless communication structure of the electric power conversion apparatus according to the first embodiment. 
         FIG. 5  is a schematic diagram illustrating a wireless communication structure of an electric power conversion apparatus according to a modification of the first embodiment. 
         FIG. 6  is a cross-sectional view of an electric power conversion apparatus according to a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Japanese Patent Application Publication No. JP 2017-139935 A discloses an electric power conversion apparatus which includes semiconductor modules each having a semiconductor element built therein and a control circuit board configured to control the semiconductor modules. In the electric power conversion apparatus, control terminals of the semiconductor modules are electrically connected to the control circuit board. 
     During the assembly of the electric power conversion apparatus disclosed in the above patent document, the control terminals of the semiconductor modules are inserted respectively into terminal insertion holes, which are formed so as to penetrate the control circuit board, and then joined to the control circuit board. However, the assembly process is troublesome because it is necessary to align the control terminals of the semiconductor modules respectively with the terminal insertion holes formed in the control circuit board. This problem becomes remarkable particularly with increase in the number of the semiconductor modules. 
     In contrast, the above-described electric power conversion apparatus according to the present disclosure has the wireless communication unit configured to wirelessly communicate electrical signals between the semiconductor module and the control circuit board. Consequently, it becomes unnecessary to connect a control terminal of the semiconductor module to the control circuit board in a wired manner. Accordingly, it becomes possible to omit a step of making a wired connection between the semiconductor module and the control circuit board from the assembly process of the electric power conversion apparatus. 
     Moreover, in the case of the electric power conversion apparatus disclosed in the above patent document, it is easy for positional deviations of the control terminals of the semiconductor modules to occur due to assembly tolerances, making the assembly process of the electric power conversion apparatus difficult. In contrast, the electric power conversion apparatus according to the present disclosure does not involve such a problem because no wired connection is necessary between the semiconductor module and the control circuit board. 
     Hence, according to the present disclosure, it becomes possible to provide an effective technique for improving the ease of assembly of an electric power conversion apparatus which includes at least one semiconductor module and a control circuit board. 
     In addition, in the electric power conversion apparatus according to the present disclosure, there are no obstacles (i.e., neither other members nor walls) on the straight path between the first and second communication devices. Consequently, it becomes possible to prevent wireless communication of electrical signals between the first and second communication devices from being disturbed by obstacles. As a result, it becomes possible to ensure the reliability of the wireless communication of electrical signals between the first and second communication devices. 
     Exemplary embodiments will be described hereinafter with reference to the drawings. It should be noted that for the sake of clarity and understanding, identical components having identical functions throughout the whole description have been marked, where possible, with the same reference numerals in the drawings and that for the sake of avoiding redundancy, explanation of identical components will not be repeated. 
     In addition, unless otherwise specified, in the drawings: a first direction representing a thickness direction of semiconductor switching elements of semiconductor modules is indicated by an arrow X; a second direction perpendicular to the first direction is indicated by an arrow Y; and a third direction perpendicular to both the first direction and the second direction is indicated by an arrow Z. 
     First Embodiment 
     As shown in  FIGS. 1 and 2 , an electric power conversion apparatus  1  according to the first embodiment includes a plurality of semiconductor modules  10 , a control circuit board  20  configured to control the semiconductor modules  10 , a wireless communication unit  30  configured to wirelessly communicate electrical signals between each of the semiconductor modules  10  and the control circuit board  20 , and a capacitor  40 . 
     The electric power conversion apparatus  1  is installed in a vehicle such as an electric vehicle or a hybrid vehicle. In the present embodiment, the electric power conversion apparatus  1  is configured as an inverter to convert DC power of a power supply B into AC power required for driving a traction motor M of the vehicle (see  FIG. 3 ). In addition, the power supply B may be implemented by, for example, a storage battery such as a lead-acid battery or a lithium-ion battery. 
     In the electric power conversion apparatus  1 , each of the semiconductor modules  10  includes a pair of semiconductor switching elements  11  (see  FIG. 3 ) for converting DC power into AC power, and a plurality of power terminals  12 . 
     Specifically, in each of the semiconductor modules  10 , the semiconductor switching elements  11  are built in a main body  10   a  of the semiconductor module  10 . Each of the semiconductor switching elements  11  is implemented by a power switching element such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). On the other hand, each of the power terminals  12  protrudes downward from the main body  10   a  in which the semiconductor switching elements  11  are built. 
     The electric power conversion apparatus  1  further includes a cooler  6  for cooling the semiconductor modules  10 . As shown in  FIG. 2 , the cooler  6  includes a plurality of cooling pipes  7  through which a coolant flows, an inflow pipe  8  connected to an inflow header portion that is common to the cooling pipes  7 , and an outflow pipe  9  connected to an outflow header portion that is common to the cooling pipes  7 . 
     The coolant may be implemented by, for example, a natural coolant such as water or ammonia, water mixed with an ethylene glycol-based antifreeze, a fluorocarbon-based coolant such as Fluorinert, HCFC123 or HFC134a, an alcohol-based coolant such as methanol or alcohol, or a ketone-based coolant such as acetone. 
     The cooling pipes  7  of the cooler  6  and the semiconductor modules  10  are stacked together to form a module stack  5 . Specifically, in the module stack  5 , the cooling pipes  7  of the cooler  6  are stacked alternately with the semiconductor modules  10  in a stacking direction; the stacking direction is parallel to an extending plane P of the control circuit board  20  (or a plane P in which the control circuit board  20  extends) and coincides with the first direction X that represents the thickness direction of the semiconductor switching elements  11  of the semiconductor modules  10 . That is, the stacking direction coincides with the thickness direction of the semiconductor switching elements  11 . In addition, the main bodies  10   a  of the semiconductor modules  10  have major surfaces thereof parallel to the semiconductor switching elements  11 ; and the normal direction of the major surfaces coincides with the thickness direction of the semiconductor switching elements  11  and thus with the stacking direction. Such an arrangement of the semiconductor modules  10  may be referred to as a “stacked arrangement”. 
     Furthermore, in the electric power conversion apparatus  1 , there is provided a pressure-applying member (not shown) to apply pressure in the first direction X to the semiconductor modules  10  each of which is sandwiched between an adjacent pair of the cooling pipes  7  of the cooler  6  in the first direction X. Consequently, each of the semiconductor modules  10  is cooled through heat exchange with the coolant flowing through the adjacent pair of the cooling pipes  7 . 
     In addition, the number of the semiconductor modules  10  is not limited to a particular number and can be changed as appropriate. On the other hand, it is preferable to set the number of the cooling pipes  7  of the cooler  6  according to the number of the semiconductor modules  10 . 
     The control circuit board  20  is configured to control the switching operation (or on/off operation) of the semiconductor switching elements  11  of the semiconductor modules  10 . The control circuit board  20  is arranged above the semiconductor modules  10  so as to face the semiconductor modules  10  through a space  2   a  formed between the control circuit board  20  and the semiconductor modules  10 . Moreover, the control circuit board  20  is formed to extend in the plane P which is defined by both the first direction X and the second direction Y that is perpendicular to the first direction X. On an upper surface  20   a  of the control circuit board  20 , there is provided an ECU  21  as a controller for controlling the semiconductor modules  10 . 
     The wireless communication unit  30  includes a plurality of first communication devices  31  and a plurality of second communication devices  32 . The first communication devices  31  are provided on the control circuit board  20  so as to face the semiconductor modules  10  in the third direction Z. Each of the second communication devices  32  is provided on a corresponding one of the semiconductor modules  10  so as to face the control circuit board  20  in the third direction Z. 
     The wireless communication unit  30  is configured to perform two-way (or bidirectional) communication between each corresponding pair of the first communication devices  31  and the second communication devices  32 . Specifically, in the present embodiment, each of the first and second communication devices  31  and  32  is configured as a transceiver. That is, when each of the first communication devices  31  functions as a transmitter to transmit (or emit) an electrical signal (also referred to as a “radio-frequency signal”), the corresponding one of the second communication devices  32  functions as a receiver to receive the electrical signal. On the other hand, when each of the second communication devices  32  functions as a transmitter to transmit an electrical signal, the corresponding one of the first communication devices  31  functions as a receiver to receive the electrical signal. 
     Moreover, in the present embodiment, to prevent wireless communication of electrical signals between the corresponding first and second communication devices  31  and  32  from being disturbed, the wireless communication unit  30  is configured so that there are no obstacles (i.e., neither other members nor walls) on straight paths between the corresponding first and second communication devices  31  and  32 . 
     The electric power conversion apparatus  1  further includes a housing  2  which is composed of a bottomed box-shaped case  3  with an opening and a cover  4  that covers the opening of the case  3 . In the case  3 , there are received the module stack  5 , the wireless communication unit  30  and a plurality of heat-generating components including the capacitor  40 . The control circuit board  20  is mounted to a part of the cover  4  which faces the semiconductor modules  10 . More specifically, a plurality of boss portions  4   b  are formed on a back surface (or interior surface)  4   a  of the cover  4 ; and the control circuit board  20  is fixed to the boss portions  4   b.  In addition, it is preferable that both the case  3  and the cover  4  are formed of a metal material having high heat conductivity, i.e., a metal material excellent in heat dissipation. 
     As shown in  FIG. 2 , each of the semiconductor modules  10  has three power terminals  12  protruding in parallel with each other from a lower surface of the main body  10   a  thereof to the lower side in the third direction Z. The three power terminals  12  include a positive-electrode terminal  12 P, a negative-electrode terminal  12 N and an output terminal  12 A. In addition, it should be noted that the arrangement and the protruding direction of the three power terminals  12  are not particularly limited. 
     Moreover, each of the semiconductor modules  10  has a pair of semiconductor switching elements  11  built in the main body  10   a  thereof. Furthermore, each of the semiconductor modules  10  has two second communication devices  32  mounted on an upper surface  10   b  of the main body  10   a  thereof in alignment with each other in the second direction Y; the upper surface  10   b  of the main body  10   a  faces the control circuit board  20 . The two second communication devices  32  are provided respectively for controlling the pair of semiconductor switching elements  11  of the semiconductor module  10 . In other words, the two second communication devices  32  respectively correspond to the pair of semiconductor switching elements  11  of the semiconductor module  10 . Moreover, the two second communication devices  32  are configured to perform wireless communication respectively with two first communication devices  31  mounted on a lower surface  20   b  of the control circuit board  20 . In other words, the two first communication devices  31  respectively correspond to the two second communication devices  32 . 
     In addition, it is preferable that the number of the first communication devices  31  and the number of the second communication devices  32  are set to be equal to each other. However, the number of the first communication devices  31  and the number of the second communication devices  32  may also be set to be different from each other as necessary. 
     As shown in  FIG. 3 , an inverter circuit formed in the electric power conversion apparatus  1  has legs of three phases (i.e., U, V and W phases) connected in parallel to each other between a positive electrode and a negative electrode of the power supply B. Each of the legs is formed of an upper-arm semiconductor switching element  11   u  and a lower-arm semiconductor switching element  11   d  that are built in the main body  10   a  of a corresponding one of the semiconductor modules  10  and connected in series with each other. The upper-arm semiconductor switching element  11   u  is electrically connected to the positive electrode of the power supply B via the positive-electrode terminal  12 P of the semiconductor module  10 , whereas the lower-arm semiconductor switching element  11   d  is electrically connected to the negative electrode of the power supply B via the negative-electrode terminal  12 N of the semiconductor module  10 . Moreover, in each of the legs, a junction point between the upper-arm semiconductor switching element  11   u  and the lower-arm semiconductor switching element  11   d  is electrically connected, via the output terminal  12 A of the semiconductor module  10 , to a corresponding one of three terminals (i.e., U-phase, V-phase and W-phase terminals) of the motor M. In addition, each of the upper-arm and lower-arm semiconductor switching elements  11   u  and  11   d  has a flyback diode (or freewheeling diode) connected in antiparallel thereto. 
       FIG. 4  illustrates a wireless communication structure of the electric power conversion apparatus  1  according to the present embodiment. As shown in  FIG. 4 , a drive IC  22  is provided, in addition to the ECU  21 , on the control circuit board  20 . 
     The drive IC  22  is electrically connected with the ECU  21  via an electrically-conductive member  23 . On the other hand, the semiconductor modules  10  are electrically connected, via electrically-conductive members  14 , with a detection unit  13  which includes sensors such as a temperature sensor and a current sensor. 
     In operation, control signals Sa are sent from the ECU  21  to the drive IC  22  through the electrically-conductive member  23 . Based on the control signals Sa, the drive IC  22  outputs gate signals Sb which are electrical signals. Then, the gate signals Sb are wirelessly transmitted by the first communication devices  31  each functioning as a transmitter to the second communication devices  32  each functioning as a receiver. Thereafter, the gate signals Sb are sent from the second communication devices  32  to gate terminals of the semiconductor switching elements  11 . Consequently, the semiconductor switching elements  11  are driven by the gate signals Sb to be turned on and off. 
     On the other hand, the detection unit  13  outputs detection signals Sc which are electrical signals indicating information detected by the sensors. Then, the detection signals Sc are sent to the semiconductor modules  10  through the electrically-conductive members  14 , and further sent to the second communication devices  32  provided on the semiconductor modules  10 . Thereafter, the detection signals Sc are wirelessly transmitted by the second communication devices  32  each functioning as a transmitter to the first communication devices  31  each functioning as a receiver. Then, the detection signals Sc are sent from the first communication devices  31  to the ECU  21 . 
     According to the present embodiment, it is possible to achieve the following advantageous effects. 
     The electric power conversion apparatus  1  according to the present embodiment has the wireless communication unit  30  configured to wirelessly communicate the electrical signals (i.e., the gate signals Sb and the detection signals Sc) between each of the semiconductor modules  10  and the control circuit board  20 . Consequently, it becomes unnecessary to connect control terminals of the semiconductor modules  10  to the control circuit board  20  in a wired manner. Accordingly, it becomes possible to omit a step of making wired connections between the semiconductor modules  10  and the control circuit board  20  from the assembly process of the electric power conversion apparatus  1 . 
     Moreover, in the case of arranging the semiconductor modules  10  in a stacked manner and connecting control terminals of the semiconductor modules  10  to the control circuit board  20  in a wired manner, it is easy for positional deviations of the control modules to occur due to assembly tolerances, making the assembly process of the electric power conversion apparatus difficult. In contrast, the electric power conversion apparatus  1  according to the present embodiment does not involve such a problem because no wired connections are necessary between the semiconductor modules  10  and the control circuit board  20 . 
     Hence, according to the present embodiment, it becomes possible to provide an effective technique for improving the ease of assembly of the electric power conversion apparatus  1  which includes the semiconductor modules  10  and the control circuit board  20 . 
     Furthermore, in the case of connecting control terminals of the semiconductor modules  10  to the control circuit board  20  in a wired manner, after the assembly process of the electric power conversion apparatus, stress may be induced in the control terminals due to relative displacement between the semiconductor modules  10  and the control circuit board  20 . In contrast, the electric power conversion apparatus  1  according to the present embodiment does not involve such a problem because no wired connections are necessary between the semiconductor modules  10  and the control circuit board  20 . Consequently, it becomes possible to ensure high vibration resistance of the electric power conversion apparatus  1 . 
     Moreover, in the electric power conversion apparatus  1  according to the present embodiment, there are no obstacles (i.e., neither other members nor walls) on straight paths between the corresponding first and second communication devices  31  and  32 . Consequently, it becomes possible to prevent wireless communication of the electrical signals (i.e., the gate signals Sb and the detection signals Sc) between the corresponding first and second communication devices  31  and  32  from being disturbed by obstacles. As a result, it becomes possible to ensure the reliability of the wireless communication of the electrical signals between the corresponding first and second communication devices  31  and  32 . 
     In the electric power conversion apparatus  1  according to the present embodiment, each of the semiconductor modules  10  has the pair of semiconductor switching elements  11  built therein. The wireless communication unit  30  includes the plurality of second communication devices  32  each corresponding to one of the semiconductor switching elements  11  of the semiconductor modules  10 , and the plurality of first communication devices  31  each corresponding to one of the plurality of second communication devices  32 . 
     In the case of connecting the semiconductor switching elements  11  of the semiconductor modules  10  to the control circuit board  20  in a wired manner, the ease of assembly of the electric power conversion apparatus may be lowered with increase in the number of the semiconductor switching elements  11  of the semiconductor modules  10 . In contrast, with the wireless communication structure of the electric power conversion apparatus  1  according to the present embodiment, it becomes possible to prevent the ease of assembly of the electric power conversion apparatus  1  from being lowered with increase in the number of the semiconductor switching elements  11  of the semiconductor modules  10 . Moreover, in the electric power conversion apparatus  1 , with increase in the number of the communication devices  31  and  32 , the reliability of the wireless communication of the electrical signals between the corresponding first and second communication devices  31  and  32  may be lowered. In this regard, in the present embodiment, the wireless communication unit  30  is configured so that there are no obstacles on straight paths between the corresponding first and second communication devices  31  and  32 . Consequently, it becomes possible to prevent the reliability of the wireless communication of the electrical signals between the corresponding first and second communication devices  31  and  32  from being lowered with increase in the number of the communication devices  31  and  32 . 
     The electric power conversion apparatus  1  according to the present embodiment includes the bottomed box-shaped case  3  in which the semiconductor modules  10  are received, and the cover  4  that covers the opening of the case  3 . The control circuit board  20  is mounted to a part of the cover  4  which faces the semiconductor modules  10 . That is, the control circuit board  20  is mounted to the cover  4  that is a separate member from the case  3  in which the semiconductor modules  10  are received. 
     With the above structure, in the case of connecting control terminals of the semiconductor modules  10  to the control circuit board  20  in a wired manner, it is difficult to correct positional deviations of the control terminals of the semiconductor modules  10  with respect to the control circuit board  20 . In contrast, with the wireless communication structure of the electric power conversion apparatus  1  according to the present embodiment, it becomes unnecessary to connect control terminals of the semiconductor modules  10  to the control circuit board  20  in a wired manner. Consequently, it becomes possible to omit the step of correcting positional deviations of the control terminals of the semiconductor modules  10  with respect to the control circuit board  20  from the assembly process of the electric power conversion apparatus  1 . As a result, it becomes possible to improve the ease of assembly of the electric power conversion apparatus  1 ; it also becomes possible to prevent stress from being induced in the control terminals due to relative displacement between the semiconductor modules  10  and the control circuit board  20 . 
     The electric power conversion apparatus  1  according to the present embodiment includes the cooler  6  configured to cool the semiconductor modules  10 . The cooler  6  includes the cooling pipes  7  through which the coolant flows. The cooling pipes  7  are stacked alternately with the semiconductor modules  10  in the stacking direction that is parallel to the extending plane P of the control circuit board  20  and coincides with the thickness direction X of the semiconductor switching elements  11  of the semiconductor modules  10 . 
     With the above stacked arrangement, it becomes possible to effectively cool the semiconductor modules  10  while realizing wireless communication between the semiconductor modules  10  and the control circuit board  20 . 
     Modification of First Embodiment 
     In the wireless communication structure according to the first embodiment, the drive IC  22  is provided, together with the ECU  21 , on the control circuit board  20  (see  FIG. 4 ). 
     In contrast, in a wireless communication structure according to the present modification, as shown in  FIG. 5 , there is no drive IC provided on the control circuit board  20 . Instead, each of the semiconductor modules  10  has a drive IC  22  provided therein. The drive IC  22  is electrically connected with the semiconductor switching elements  11  of the semiconductor module  10  via electrically-conductive members  24 . 
     In operation, the ECU  21  outputs control signals Sa which are electrical signals. Then, the control signals Sa are wirelessly transmitted by the first communication devices  31  each functioning as a transmitter to the second communication devices  32  each functioning as a receiver. Thereafter, the control signals Sa are sent from the second communication devices  32  to the drive ICs  22  of the semiconductor modules  10 . Based on the control signals Sa, the drive ICs  22  output gate signals Sb. Then, the gate signals Sb are sent to the gate terminals of the semiconductor switching elements  11  through the electrically-conductive members  24 . Consequently, the semiconductor switching elements  11  are driven by the gate signals Sb to be turned on and off. 
     On the other hand, the detection unit  13  outputs the detection signals Sc which are electrical signals indicating information detected by the sensors. Then, the detection signals Sc are sent to the semiconductor modules  10  through the electrically-conductive members  14 , and further sent to the drive ICs  22  through electrically-conductive members  25 . Thereafter, the detection signals Sc are further sent to the second communication devices  32  provided on the semiconductor modules  10 . Then, the detection signals Sc are wirelessly transmitted by the second communication devices  32  each functioning as a transmitter to the first communication devices  31  each functioning as a receiver. Thereafter, the detection signals Sc are sent from the first communication devices  31  to the ECU  21 . 
     With the above wireless communication structure according to the present modification, it is also possible to achieve the same advantageous effects as achievable with the wireless communication structure according to the first embodiment. 
     Second Embodiment 
     An electric power conversion apparatus  101  according to the second embodiment has a similar configuration to the electric power conversion apparatus  1  according to the first embodiment. Therefore, the differences therebetween will be mainly described hereinafter. 
       FIG. 6  illustrates the configuration of the electric power conversion apparatus  101  according to the present embodiment. Compared to the electric power conversion apparatus  1  according to the first embodiment (see  FIG. 1 ), the electric power conversion apparatus  101  according to the present embodiment differs in the arrangement of the semiconductor modules  10 . 
     Specifically, as shown in  FIG. 6 , in the electric power conversion apparatus  101  according to the present embodiment, the semiconductor modules  10  are arranged in alignment with each other in an alignment direction; the alignment direction is parallel to the extending plane P of the control circuit board  20  and coincides with the second direction Y that is perpendicular to the first direction X representing the thickness direction of the semiconductor switching elements  11  of the semiconductor modules  10 . That is, the alignment direction is perpendicular to the thickness direction of the semiconductor switching elements  11 . Moreover, the normal direction of the major surfaces of the main bodies  10   a  of the semiconductor modules  10  is perpendicular to the alignment direction. Such an arrangement of the semiconductor modules  10  may be referred to as a “planar arrangement”. 
     Moreover, the electric power conversion apparatus  101  according to the present embodiment includes a wireless communication unit  130 . The wireless communication unit  130  has a plurality of first communication devices  31  mounted on the lower surface  20   b  of the control circuit board  20  and a plurality of second communication devices  32  each of which is mounted on the upper surface  10   b  of the main body  10   a  of a corresponding one of the semiconductor modules  10 . 
     Furthermore, the electric power conversion apparatus  101  according to the present embodiment includes a cooler  6  that is arranged under a partition wall  3   a  of the case  3  to cool the semiconductor modules  10 . The semiconductor modules  10  are arranged on an upper surface of the partition wall  3   a  and thus separated from the cooler  6  by the partition wall  3   a.  Moreover, in the cooler  6 , there is formed a cooling space  6   a  through which a coolant flows. Furthermore, the cooler  6  has an inflow pipe  8  connected to the upstream side of the cooling space  6   a  and an outflow pipe  9  connected to the downstream side of the cooling space  6   a.    
     In addition, the electric power conversion apparatus  101  according to the present embodiment may have either the wireless communication structure shown in  FIG. 4  or the wireless communication structure shown in  FIG. 5 . 
     According to the present embodiment, it is possible to achieve the following advantageous effects. 
     In the case of arranging the semiconductor modules  10  in a planar manner and connecting control terminals of the semiconductor modules  10  to the control circuit board  20  in a wired manner, it is easy for positional deviations of the control modules to occur due to large intervals between the adjacent semiconductor modules  10  in the second direction Y, making the assembly process of the electric power conversion apparatus difficult. In contrast, the electric power conversion apparatus  101  according to the present embodiment does not involve such a problem because no wired connections are necessary between the semiconductor modules  10  and the control circuit board  20 . 
     Hence, according to the present embodiment, it becomes possible to improve the ease of assembly of the electric power conversion apparatus  101 , which has the semiconductor modules  10  arranged in the planar manner, while realizing wireless communication between the semiconductor modules  10  and the control circuit board  20 . 
     While the above particular embodiments have been shown and described, it will be understood by those skilled in the art that various modifications, changes and improvements may be made without departing from the spirit of the present disclosure. 
     For example, in the second embodiment, the electric power conversion apparatus  101  includes the cooler  6  for cooling the semiconductor modules  10 . However, the cooler  6  may be omitted from the configuration of the electric power conversion apparatus  101  in cases where it is unnecessary to cool the semiconductor modules  10  or the electric power conversion apparatus  101  employs a cooling element instead of the cooler  6 . 
     In the above-described embodiments, each of the semiconductor modules  10  has a pair of semiconductor switching elements  11  built therein. However, each of the semiconductor modules  10  may have only one semiconductor element or three or more semiconductor elements built therein. 
     In the above-described embodiments, the control circuit board  20  is mounted to the cover  4  that covers the opening of the case  3 . However, the control circuit board  20  may alternatively be mounted to the case  3 . 
     In the above-described embodiments, the wireless communication unit  30  (or  130 ) is configured to perform two-way communication between each corresponding pair of the first communication devices  31  and the second communication devices  32 . However, the wireless communication unit  30  (or  130 ) may alternatively be configured to perform only one-way communication between each corresponding pair of the first communication devices  31  and the second communication devices  32 . For example, each of first communication devices  31  may be configured to function only as a transmitter; and each of the second communication devices  32  may be configured to function only as a receiver. Otherwise, each of first communication devices  31  may be configured to function only as a receiver; and each of the second communication devices  32  may be configured to function only as a transmitter. 
     In the above-described embodiments, each of the first communication devices  31  is mounted on the lower surface  20   b  of the control circuit board  20 ; and each of the second communication devices  32  is mounted on the upper surface  10   b  of the main body  10   a  of a corresponding one of the semiconductor modules  10 . However, the mounting locations of the first and second communication devices  31  and  32  are not particularly limited. For example, each of the first communication devices  31  may alternatively be mounted on the upper surface  20   a  of the control circuit board  20 ; and each of the second communication devices  32  may alternatively be mounted on a side surface of the main body  10   a  of a corresponding one of the semiconductor modules  10 .