<?php
$primaryCat = new WPSEO_Primary_Term('category', get_the_ID());
$primaryCat = $primaryCat->get_primary_term();
$primaryCat = get_cat_name($primaryCat);

$categories = get_the_category();
foreach( $categories as $category ) {
   $defaultCat = $category->name;
   $defaultCatLink = get_category_link( $category->term_id );
}

if ( $primaryCat !== "" ) {
   $cat = new WPSEO_Primary_Term('category', get_the_ID());
   $cat = $cat->get_primary_term();

   $catName = get_cat_name($cat);
   $catLink = get_category_link($cat);

} else {
   $catName = $defaultCat;
   $catLink = $defaultCatLink;
}
?>

<h3><a href="<?php echo $catLink; ?>"><?php echo $catName; ?></a></h3>