A power conversion system comprising: a rectifier comprising at least one rectifier switch module for rectifying AC input power; a DC bus connected to the rectifier; wherein said at least one rectifier switch module comprises: a base plate ; a housing connected to the base plate, the housing including side walls and a top wall and defining an interior space that contains at least one semiconductor switch ; a protective cover layer comprising a corrosion protection material , said protective cover layer extending between the side walls and dividing the interior space into an inner sub-space located between the base plate and the protective cover layer and an outer sub-space located between the protective cover layer and the top wall of the housing; a seam defined between said base plate and the side walls of said housing; and a seal located in said seam, wherein said seal comprises said corrosion protection material; wherein said at least one semiconductor switch is located in said inner sub-space such that an atmosphere in said outer sub-space passes through the protective cover layer of corrosion protection material before entering said inner sub-space. a rectifier comprising at least one rectifier switch module for rectifying AC input power; a DC bus connected to the rectifier; wherein said at least one rectifier switch module comprises: a base plate ; a housing connected to the base plate, the housing including side walls and a top wall and defining an interior space that contains at least one semiconductor switch ; a protective cover layer comprising a corrosion protection material , said protective cover layer extending between the side walls and dividing the interior space into an inner sub-space located between the base plate and the protective cover layer and an outer sub-space located between the protective cover layer and the top wall of the housing; a seam defined between said base plate and the side walls of said housing; and a seal located in said seam, wherein said seal comprises said corrosion protection material; wherein said at least one semiconductor switch is located in said inner sub-space such that an atmosphere in said outer sub-space passes through the protective cover layer of corrosion protection material before entering said inner sub-space. a base plate ; a housing connected to the base plate, the housing including side walls and a top wall and defining an interior space that contains at least one semiconductor switch ; a protective cover layer comprising a corrosion protection material , said protective cover layer extending between the side walls and dividing the interior space into an inner sub-space located between the base plate and the protective cover layer and an outer sub-space located between the protective cover layer and the top wall of the housing; a seam defined between said base plate and the side walls of said housing; and a seal located in said seam, wherein said seal comprises said corrosion protection material; wherein said at least one semiconductor switch is located in said inner sub-space such that an atmosphere in said outer sub-space passes through the protective cover layer of corrosion protection material before entering said inner sub-space. <EOS>