PHP Experts for the_excerpt

May be a difficult problem for someone who does not support PHP:
output in a list THE EXCERPT instead of the category for costum post type in a list.

This is regulated in a PHP file:

$terms = wp_get_post_terms(get_the_ID(), 'portfolio_category');

$k = 1;
            foreach ($terms as $term) {
                $html .= "$term->name";
                if (count($terms) != $k) {
                    $html .= ', ';
                }
                $k++;
            }

Works fine. But I cant change it to the post excerpt with this. It works, but spits all content of all posts of “portfolio_category” and the excerpts out:

$my_excerpt = get_the_excerpt();
	if ( $my_excerpt != '' ) {
	/ Some string manipulation performed
	}
	echo $my_excerpt;

What is to do?
Thanks a lot!

Mark from Hamburg, Germany