Event log checking excel

$Date = Get-Date
$Range = $Date.addDays(-1)
$Unique = $Unique | Select -Unique

Get-Winevent -FilterHashtable @{LogName="System","Application"; Level=1,2,3; startTime=$range} | Select-Object @{ expression={$_.LevelDisplayName}; label='Level' }, Message, @{ expression={$_.ID}; label='EventID' },  @{ expression={$_.LogName}; label='Log' }, @{ expression={$_.MachineName}; label='Server' }, @{ expression={$_.TimeCreated}; label='Created' } | export-csv "C:\scripts\sysevents.csv" -NoTypeInformation

The code shown here is a mash up of ones from the internet but it gets the job done. I want to expand it slightly.

I wish for the event log to search the previous days excel sheet and ONLY add ones that are not on it. I know you can compare .csv files but not sure how I would do it. If someone could point me in the right direction that be awesome!

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