[xsl] removing comma from within sum command

Is there a way to remove commas from the Charge node in this select?
placing translate around charge seems to cause an error.: " NodeTest expected here."

<xsl:value-of select="format-number(sum(Trade/Step
   [concat(substring(MinFlowDate,7),substring(MinFlowDate,1,2),substring(MinFlowDate,4,2))&gt;=
concat(substring($global,7)+3,substring($global,1,2),substring($global,4,2))]

   [concat(substring(MinFlowDate,7),substring(MinFlowDate,1,2),substring(MinFlowDate,4,2))&lt;
concat(substring($global,7)+6,substring($global,1,2),substring($global,4,2))]
   /Charge), '###,###,##0')"/>



Thanks,
Dmitri