Function Add-ConditionalFormatting {
    <#
      .Synopsis
        Adds contitional formatting to worksheet.
      .Example
        $excel = $avdata | Export-Excel -Path (Join-path $FilePath "\Machines.XLSX" ) -WorksheetName "Server Anti-Virus" -AutoSize -FreezeTopRow -AutoFilter -PassThru

        Add-ConditionalFormatting -WorkSheet $excel.Workbook.Worksheets[1] -Address "b2:b1048576" -ForeGroundColor "RED"     -RuleType ContainsText -ConditionValue "2003"
        Add-ConditionalFormatting -WorkSheet $excel.Workbook.Worksheets[1] -Address "i2:i1048576" -ForeGroundColor "RED"     -RuleType ContainsText -ConditionValue "Disabled"
        $excel.Workbook.Worksheets[1].Cells["D1:G1048576"].Style.Numberformat.Format = [cultureinfo]::CurrentCulture.DateTimeFormat.ShortDatePattern
        $excel.Workbook.Worksheets[1].Row(1).style.font.bold = $true
        $excel.Save() ; $excel.Dispose()

        Here Export-Excel is called with the -passThru parameter so the Excel Package object is stored in $Excel
        The desired worksheet is selected and the then columns B and i are conditially formatted (excluding the top row) to show red text if 
        the columns contain "2003" or "Disabled respectively. A fixed date formats are then applied to columns D..G, and the top row is formatted.
        Finally the workbook is saved and the Excel object closed.

    #>
    Param (
        #The worksheet where the format is to be applied
        [Parameter(Mandatory = $true, ParameterSetName = "NamedRule")]
        [Parameter(Mandatory = $true, ParameterSetName = "DataBar")]
        [Parameter(Mandatory = $true, ParameterSetName = "ThreeIconSet")]
        [Parameter(Mandatory = $true, ParameterSetName = "FourIconSet")]
        [Parameter(Mandatory = $true, ParameterSetName = "FiveIconSet")]
        [OfficeOpenXml.ExcelWorksheet]$WorkSheet ,
        #The area of the worksheet where the format is to be applied
        [Parameter(Mandatory = $true, ParameterSetName = "NamedRule")]
        [Parameter(Mandatory = $true, ParameterSetName = "DataBar")]
        [Parameter(Mandatory = $true, ParameterSetName = "ThreeIconSet")]
        [Parameter(Mandatory = $true, ParameterSetName = "FourIconSet")]
        [Parameter(Mandatory = $true, ParameterSetName = "FiveIconSet")]
        [OfficeOpenXml.ExcelAddress]$Range ,
        #One or more row(s), Column(s) and/or block(s) of cells to format
        [Parameter(Mandatory = $true, ParameterSetName = "NamedRuleAddress")]
        [Parameter(Mandatory = $true, ParameterSetName = "DataBarAddress")]
        [Parameter(Mandatory = $true, ParameterSetName = "ThreeIconSetAddress")]
        [Parameter(Mandatory = $true, ParameterSetName = "FourIconSetAddress")]
        [Parameter(Mandatory = $true, ParameterSetName = "FiveIconSetAddress")]
        $Address ,
        #One of the standard named rules - Top / Bottom / Less than / Greater than / Contains etc
        [Parameter(Mandatory = $true, ParameterSetName = "NamedRule", Position = 3)]
        [Parameter(Mandatory = $true, ParameterSetName = "NamedRuleAddress", Position = 3)]
        [OfficeOpenXml.ConditionalFormatting.eExcelConditionalFormattingRuleType]$RuleType ,
        #Text colour for matching objects
        [Alias("ForeGroundColour")]
        [System.Drawing.Color]$ForeGroundColor,
        #colour for databar type charts
        [Parameter(Mandatory = $true, ParameterSetName = "DataBar")]
        [Parameter(Mandatory = $true, ParameterSetName = "DataBarAddress")]
        [Alias("DataBarColour")]
        [System.Drawing.Color]$DataBarColor,
        #One of the three-icon set types (e.g. Traffic Lights)
        [Parameter(Mandatory = $true, ParameterSetName = "ThreeIconSet")]
        [Parameter(Mandatory = $true, ParameterSetName = "ThreeIconSetAddress")]
        [OfficeOpenXml.ConditionalFormatting.eExcelconditionalFormatting3IconsSetType]$ThreeIconsSet,
        #A four-icon set name
        [Parameter(Mandatory = $true, ParameterSetName = "FourIconSet")]
        [Parameter(Mandatory = $true, ParameterSetName = "FourIconSetAddress")]
        [OfficeOpenXml.ConditionalFormatting.eExcelconditionalFormatting4IconsSetType]$FourIconsSet,
        #A five-icon set name
        [Parameter(Mandatory = $true, ParameterSetName = "FiveIconSet")]
        [Parameter(Mandatory = $true, ParameterSetName = "FiveIconSetAddress")]
        [OfficeOpenXml.ConditionalFormatting.eExcelconditionalFormatting5IconsSetType]$FiveIconsSet,
        #A value for the condition (e.g. "2000" if the test is 'lessthan 2000')
        [string]$ConditionValue,
        #A second value for the conditions like between x and Y
        [string]$ConditionValue2,
        #Background colour for matching items
        [System.Drawing.Color]$BackgroundColor,
        #Background pattern for matching items
        [OfficeOpenXml.Style.ExcelFillStyle]$BackgroundPattern = [OfficeOpenXml.Style.ExcelFillStyle]::None ,
        #Secondary colour when a background pattern requires it
        [System.Drawing.Color]$PatternColor,
        #Sets the numeric format for matching items
        $NumberFormat,
        #Put matching items in bold face
        [switch]$Bold,
        #Put matching items in italic
        [switch]$Italic,
        #Underline matching items
        [switch]$Underline,
        #Strikethrough text of matching items
        [switch]$StrikeThru
    )
    #Allow conditional formatting to work like Set-Format (with single ADDRESS parameter), split it to get worksheet and range of cells.  
    If ($Address -and -not $WorkSheet -and -not $Range) {
        $WorkSheet = $Address.Worksheet[0]
        $Range     = $Address.Address 
    }    
    If ($ThreeIconsSet) {$rule = $WorkSheet.ConditionalFormatting.AddThreeIconSet($Range , $ThreeIconsSet)}
    elseif ($FourIconsSet) {$rule = $WorkSheet.ConditionalFormatting.AddFourIconSet( $Range , $FourIconsSet) }
    elseif ($FiveIconsSet) {$rule = $WorkSheet.ConditionalFormatting.AddFiveIconSet( $Range , $IconType)     }
    elseif ($DataBarColor) {$rule = $WorkSheet.ConditionalFormatting.AddDatabar(     $Range , $DataBarColor) }
    else {                  $rule = ($WorkSheet.ConditionalFormatting)."Add$RuleType"($Range)}

    if ($ConditionValue -and $RuleType -match "Top|Botom") {$rule.Rank = $ConditionValue }
    if ($ConditionValue -and $RuleType -match "StdDev") {$rule.StdDev = $ConditionValue }
    if ($ConditionValue -and $RuleType -match "Than|Equal|Expression") {$rule.Formula = $ConditionValue }
    if ($ConditionValue -and $RuleType -match "Text|With") {$rule.Text = $ConditionValue }
    if ($ConditionValue -and
        $ConditionValue2 -and $RuleType -match "Between") {
        $rule.Formula = $ConditionValue
        $rule.Formula2 = $ConditionValue2
    }

    if ($NumberFormat) {$rule.Style.NumberFormat.Format = $NumberFormat }
    if ($Underline) {$rule.Style.Font.Underline = [OfficeOpenXml.Style.ExcelUnderLineType]::Single }
    if ($Bold) {$rule.Style.Font.Bold = $true}
    if ($Italic) {$rule.Style.Font.Italic = $true}
    if ($StrikeThru) {$rule.Style.Font.Strike = $true}
    if ($ForeGroundColor) {$rule.Style.Font.Color.color = $ForeGroundColor   }
    if ($BackgroundColor) {$rule.Style.Fill.BackgroundColor.color = $BackgroundColor   }
    if ($BackgroundPattern) {$rule.Style.Fill.PatternType = $BackgroundPattern }
    if ($PatternColor) {$rule.Style.Fill.PatternColor.color = $PatternColor      }
}