this application is based on an application no . 2006 - 195585 filed jul . 18 , 2006 in japan , the disclosure of which is incorporated herein by reference . fig1 is a plan view showing an example of an internal configuration of a power semiconductor module according to a first embodiment of the present invention . fig2 is a circuit diagram relevant to a phase - w circuit of the power semiconductor module of fig1 . here , exemplified is a case of converting unipolar power , which is rectified from ac power , into three - phase ac power ( phase - u , phase - v , phase - w ). the power semiconductor module m is provided with frames f 1 to f 5 made of electrically conductive material on an electrically insulating substrate , and an additional frame f 6 is arranged close to the frame f 2 . the frames f 1 and f 5 are fed with external unipolar power . for example , a terminal p of the frame f 1 is connected with a positive line of an ac power rectifying circuit , while a terminal n of the frame f 5 is connected with a negative line of the ac power rectifying circuit . a terminal w of the frame f 2 outputs the phase - w of ac power to an external circuit . a terminal v of the frame f 3 outputs the phase - v of ac power to an external circuit . a terminal u of the frame f 4 outputs the phase - u of ac power to an external circuit . on the frame f 1 , mounted are switching devices s 4 to s 6 , such as igbt ( insulated gate bipolar transistor ), and flywheel diodes d 4 to d 6 . the collectors of the switching devices s 4 to s 6 and the cathodes of the diodes d 4 to d 6 are electrically connected to the frame f 1 . the emitter of the switching device s 4 and the anode of the diode d 4 are connected to each other using a short connecting wire , and also to the frame f 4 using a relatively longer connecting wire l 4 . likewise , the emitter of the switching device s 5 and the anode of the diode d 5 are connected to each other using a short connecting wire , and also to the frame f 3 using a relatively longer connecting wire l 5 . further , the emitter of the switching device s 6 and the anode of the diode d 6 are connected to each other using a short connecting wire , and also to the frame f 2 using a relatively longer connecting wire l 6 . meanwhile , on the frame f 2 , mounted are a switching device s 3 , such as igbt , and a flywheel diodes d 3 . the collector of the switching device s 3 and the cathode of the diode d 3 are electrically connected to the frame f 2 . the emitter of the switching device s 3 and the anode of the diode d 3 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 3 . on the frame f 3 , mounted are a switching device s 2 , such as igbt , and a flywheel diodes d 2 . the collector of the switching device s 2 and the cathode of the diode d 2 are electrically connected to the frame f 3 . the emitter of the switching device s 2 and the anode of the diode d 2 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 2 . on the frame f 4 , mounted are a switching device s 1 , such as igbt , and a flywheel diodes d 1 . the collector of the switching device s 1 and the cathode of the diode d 1 are electrically connected to the frame f 4 . the emitter of the switching device s 1 and the anode of the diode d 1 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 1 . in this embodiment , the additional frame f 6 is electrically connected to the anode of the diode d 3 using a branching wire j 1 which branches from the connecting wire l 3 . incidentally , for avoiding complexity of the drawing , illustration of the respective gate of the respective igbt and the respective wire connected with each gate is omitted . in this configuration , the switching devices s 6 and s 3 are series - connected between the frames f 1 and f 5 , which are fed with unipolar power , to control the phase - w of ac power . the switching devices s 5 and s 2 are series - connected to control the phase - v of ac power . the switching devices s 4 and s 1 are series - connected to control the phase - u of ac power . in this embodiment , as shown in fig2 , an external snubber circuit sn 2 is connected between the terminal w of the frame f 2 for outputting the phase - w and a terminal t 1 of the additional frame f 6 . hence , the snubber circuit sn 2 resides in the closed loop circuit including the terminal t 1 , the frame f 6 , the branching wire j 1 , the switching device s 3 ( diode d 3 ), the frame f 2 and the terminal w . in the conventional power semiconductor module , on the other hand , as shown in fig7 and 8 , the snubber circuit sn 2 resides in the closed loop circuit including the terminal n , the frame f 5 , the connecting wire l 3 , the switching device s 3 ( diode d 3 ), the frame f 2 and the terminal w . therefore , this embodiment can reduce wiring length and loop area of the closed loop circuit including the snubber circuit sn 2 , thereby improving the effect of the snubber circuit sn 2 for suppressing surge voltage . here , surge suppression of the phase - w of ac power has been described in detail . likewise , in case of the phase - u of ac power , an additional frame is arranged close to the frame f 4 , and a branching wire is connected between the frame and the diode d 1 , and an external snubber circuit is connected between a terminal of the frame and the terminal u of the frame f 4 , resulting in the same effect as in phase - w . moreover , in case of the phase - v of ac power , an additional frame is arranged close to the frame f 3 , and a branching wire is connected between the frame and the diode d 2 , and an external snubber circuit is connected between a terminal of the frame and the terminal v of the frame f 3 , resulting in the same effect as in phase - w . in the above description , discussed was the closed loop circuit of the snubber circuit sn 2 which was connected between the respective frames f 2 to f 4 for outputting ac power and the frame f 5 which is a negative line of unipolar power . similarly , another closed loop circuit of a snubber circuit sn 1 which is connected between the respective frames f 2 to f 4 and the frame f 1 which is a positive line of unipolar power can be improved . fig3 is a plan view showing an example of an internal configuration of a power semiconductor module according to a second embodiment of the present invention . fig4 is a circuit diagram relevant to a phase - w circuit of the power semiconductor module of fig3 . here , exemplified is a case of converting unipolar power , which is rectified from ac power , into three - phase ac power ( phase - u , phase - v , phase - w ). the power semiconductor module m is provided with frames f 1 to f 5 made of electrically conductive material on an electrically insulating substrate , and an additional frame f 7 is arranged close to the frame f 5 . the frames f 1 and f 5 are fed with external unipolar power . for example , a terminal p of the frame f 1 is connected with a positive line of an ac power rectifying circuit , while a terminal n of the frame f 5 is connected with a negative line of the ac power rectifying circuit . a terminal w of the frame f 2 outputs the phase - w of ac power to an external circuit . a terminal v of the frame f 3 outputs the phase - v of ac power to an external circuit . a terminal u of the frame f 4 outputs the phase - u of ac power to an external circuit . on the frame f 1 , mounted are switching devices s 4 to s 6 , such as igbt , and flywheel diodes d 4 to d 6 . the collectors of the switching devices s 4 to s 6 and the cathodes of the diodes d 4 to d 6 are electrically connected to the frame f 1 . the emitter of the switching device s 4 and the anode of the diode d 4 are connected to each other using a short connecting wire , and also to the frame f 4 using a relatively longer connecting wire l 4 . likewise , the emitter of the switching device s 5 and the anode of the diode d 5 are connected to each other using a short connecting wire , and also to the frame f 3 using a relatively longer connecting wire l 5 . further , the emitter of the switching device s 6 and the anode of the diode d 6 are connected to each other using a short connecting wire , and also to the frame f 2 using a relatively longer connecting wire l 6 . meanwhile , on the frame f 2 , mounted are a switching device s 3 , such as igbt , and a flywheel diodes d 3 . the collector of the switching device s 3 and the cathode of the diode d 3 are electrically connected to the frame f 2 . the emitter of the switching device s 3 and the anode of the diode d 3 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 3 . on the frame f 3 , mounted are a switching device s 2 , such as igbt , and a flywheel diodes d 2 . the collector of the switching device s 2 and the cathode of the diode d 2 are electrically connected to the frame f 3 . the emitter of the switching device s 2 and the anode of the diode d 2 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 2 . on the frame f 4 , mounted are a switching device s 1 , such as igbt , and a flywheel diodes d 1 . the collector of the switching device s 1 and the cathode of the diode d 1 are electrically connected to the frame f 4 . the emitter of the switching device s 1 and the anode of the diode d 1 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 1 . in this embodiment , the additional frame f 7 is electrically connected to the frame f 2 using a branching wire j 2 . incidentally , for avoiding complexity of the drawing , illustration of the respective gate of the respective igbt and the respective wire connected with each gate is omitted . in this configuration , the switching devices s 6 and s 3 are series - connected between the frames f 1 and f 5 , which are fed with unipolar power , to control the phase - w of ac power . the switching devices s 5 and s 2 are series - connected to control the phase - v of ac power . the switching devices s 4 and s 1 are series - connected to control the phase - u of ac power . in this embodiment , as shown in fig4 , an external snubber circuit sn 2 is connected between the terminal n of the frame f 5 and a terminal t 2 of the additional frame f 7 . hence , the snubber circuit sn 2 resides in the closed loop circuit including the terminal t 2 , the frame f 7 , the branching wire j 2 , the switching device s 3 ( diode d 3 ), the connecting wire l 3 , the frame f 5 and the terminal n . therefore , this embodiment can reduce wiring length and loop area of the closed loop circuit including the snubber circuit sn 2 , thereby improving the effect of the snubber circuit sn 2 for suppressing surge voltage . here , surge suppression of the phase - w of ac power has been described in detail . likewise , in case of both the phase - u and the phase - v of ac power , respective additional frames are arranged close to the frame f 5 , and respective branching wires are connected between the respective frames and the frames f 3 and f 4 , and respective external snubber circuits are connected between each terminal of the respective frames and the terminal n of the frame f 5 , resulting in the same effect as in phase - w . in the above description , discussed was the closed loop circuit of the snubber circuit sn 2 which was connected between the respective frames f 2 to f 4 for outputting ac power and the frame f 5 which is a negative line of unipolar power . similarly , another closed loop circuit of a snubber circuit sn 1 which is connected between the respective frames f 2 to f 4 and the frame f 1 which is a positive line of unipolar power can be improved . fig5 is a plan view showing an example of an internal configuration of a power semiconductor module according to a third embodiment of the present invention . fig6 is a circuit diagram relevant to a phase - w circuit of the power semiconductor module of fig5 . here , exemplified is a case of converting unipolar power , which is rectified from ac power , into three - phase ac power ( phase - u , phase - v , phase - w ). the power semiconductor module m is provided with frames f 1 to f 5 made of electrically conductive material on an electrically insulating substrate , and an additional frame f 8 is arranged close to the frame f 1 . the frames f 1 and f 5 are fed with external unipolar power . for example , a terminal p of the frame f 1 is connected with a positive line of an ac power rectifying circuit , while a terminal n of the frame f 5 is connected with a negative line of the ac power rectifying circuit . a terminal w of the frame f 2 outputs the phase - w of ac power to an external circuit . a terminal v of the frame f 3 outputs the phase - v of ac power to an external circuit . a terminal u of the frame f 4 outputs the phase - u of ac power to an external circuit . on the frame f 1 , mounted are switching devices s 4 to s 6 , such as igbt , and flywheel diodes d 4 to d 6 . the collectors of the switching devices s 4 to s 6 and the cathodes of the diodes d 4 to d 6 are electrically connected to the frame f 1 . the emitter of the switching device s 4 and the anode of the diode d 4 are connected to each other using a short connecting wire , and also to the frame f 4 using a relatively longer connecting wire l 4 . likewise , the emitter of the switching device s 5 and the anode of the diode d 5 are connected to each other using a short connecting wire , and also to the frame f 3 using a relatively longer connecting wire l 5 . further , the emitter of the switching device s 6 and the anode of the diode d 6 are connected to each other using a short connecting wire , and also to the frame f 2 using a relatively longer connecting wire l 6 . meanwhile , on the frame f 2 , mounted are a switching device s 3 , such as igbt , and a flywheel diodes d 3 . the collector of the switching device s 3 and the cathode of the diode d 3 are electrically connected to the frame f 2 . the emitter of the switching device s 3 and the anode of the diode d 3 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 3 . on the frame f 3 , mounted are a switching device s 2 , such as igbt , and a flywheel diodes d 2 . the collector of the switching device s 2 and the cathode of the diode d 2 are electrically connected to the frame f 3 . the emitter of the switching device s 2 and the anode of the diode d 2 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 2 . on the frame f 4 , mounted are a switching device s 1 , such as igbt , and a flywheel diodes d 1 . the collector of the switching device s 1 and the cathode of the diode d 1 are electrically connected to the frame f 4 . the emitter of the switching device s 1 and the anode of the diode d 1 are connected to each other using a short connecting wire , and also to the frame f 5 using a relatively longer connecting wire l 1 . in this embodiment , the additional frame f 8 is electrically connected to the frame f 5 using a branching wire j 3 . incidentally , for avoiding complexity of the drawing , illustration of the respective gate of the respective igbt and the respective wire connected with each gate is omitted . in this configuration , the switching devices s 6 and s 3 are series - connected between the frames f 1 and f 5 , which are fed with unipolar power , to control the phase - w of ac power . the switching devices s 5 and s 2 are series - connected to control the phase - v of ac power . the switching devices s 4 and s 1 are series - connected to control the phase - u of ac power . in this embodiment , as shown in fig6 , an external snubber circuit sn 3 is connected between the terminal p of the frame f 1 and a terminal t 3 of the additional frame f 8 . hence , the snubber circuit sn 3 resides in the closed loop circuit including the terminal t 3 , the frame f 8 , the branching wire j 3 , the pair of switching devices , the frame f 1 and the terminal p . in the conventional power semiconductor module , on the other hand , as shown in fig7 and 8 , the snubber circuit sn 3 resides in the closed loop circuit including the terminal n , the frame f 5 , the pair of switching devices , the frame f 1 and the terminal p . therefore , this embodiment can reduce wiring length and loop area of the closed loop circuit including the snubber circuit sn 3 , thereby improving the effect of the snubber circuit sn 3 for suppressing surge voltage . in the above description , discussed was the case where the additional frame f 8 was arranged close to the frame f 1 which was a positive line of unipolar power , and the snubber circuit sn 3 was connected therebetween . similarly , the other case where an additional frame is arranged close to the frame f 5 which is a negative line of unipolar power , and the snubber circuit sn 3 is connected therebetween can be improved . although the present invention has been fully described in connection with the preferred embodiments thereof and the accompanying drawings , it is to be noted that various changes and modifications are apparent to those skilled in the art . such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom .