---

$user  = "ivanov"
$start = (Get-Date).AddDays(-7)
$dcs   = (Get-ADDomainController -Filter *).HostName

$events = foreach ($dc in $dcs) {
    Get-WinEvent -ComputerName $dc -FilterHashtable @{
        LogName   = 'Security'
        Id        = 4624, 4625, 4768, 4776
        StartTime = $start
    } -ErrorAction SilentlyContinue |
    Where-Object { $_.Message -match $user }
}

$events | Select TimeCreated, Id, MachineName, Message