3-level inverter apparatus

Abstract

A 3-level inverter includes a plurality of power semiconductor switching elements respectively connected in serial relation, a diode connected in reverse parallel relation with each of the plurality of power semiconductor switching element, and a plurality of snubber circuits for protecting the plurality of power semiconductor switching elements. The number of the snubber circuits is smaller by one as compared with the number of the power semiconductor switching circuits, and one of the snubber circuits is connected with a DC neutral point and AC output terminal. The one of the snubber circuits which is connected with the DC neutral point and the AC output terminal is a circuit including a capacitor connected in serial relation with a resistor.

What is claimed is:  
     
         1 . A 3-level inverter comprising: 
 a plurality of power semiconductor switching elements respectively connected in serial relation;    a diode connected in reverse parallel relation with each of said plurality of power semiconductor switching elements; and    a plurality of snubber circuits for protecting said plurality of power semiconductor switching elements;    wherein the number of said plurality of snubber circuits is smaller by one as compared with the number of said plurality of power semiconductor switching circuits, one of said plurality of snubber circuits being connected with a DC neutral point and AC output terminal; and    wherein said one of a plurality of snubber circuits connected with said DC neutral point and said AC output terminal is a circuit including a capacitor connected in serial relation with a resistor relation.    
     
     
         2 . A 3-level inverter according to  claim 1 , wherein said plurality of snubber circuits include a snubber circuit connected with positive potential of a DC power source and a DC neutral point, and a snubber circuit connected with negative potential of a DC power source and a DC neutral point.  
     
     
         3 . A 3-level inverter according to  claim 1 , wherein said plurality of power semiconductor switching elements are composed of 4 IGBTs.  
     
     
         4 . A 3-level inverter according to  claim 1 , wherein said plurality of power semiconductor switching elements are composed of 4 MOSFETs.  
     
     
         5 . A 3-level inverter according to  claim 1 , wherein said 3-level inverter is a power transducer for driving an AC electric motor.