New-SpIdentityProvider Add FBA users with Powwershell

Hi

i´m trying to add FBA users to a sites using power shell, and i´m using:

$web = Get-SPWweb http://url

$user = New-SPUser -UserAlias (New-SpClaimsPrincipal -Identity name@example.com -IdentityType $ip ).ToEncodedString() -Web $web

where as found in get-help New-SPClaimsPrincipal

$ip = New-SPIdentityProvider -ASPNetMembershipProvider "myMembershipProvider" -ASPNetRoleProvider "myRoleProvider"

but i could not found New-SpidentityProvider on my powershell

Thanks