<?php
//orig string
$test = 'ZZZZZW';
var_dump($test);

//convert from base36 to number.
$test = base_convert($test, 36, 10);
var_dump($test);

//increment
$test++;
var_dump($test);

//convert back (and upper case)
$test = strtoupper(base_convert($test, 10, 36));
var_dump($test);
?>