iconv()在laravel编码问题

下面是个获取汉子拼音首字母的函数，laravel控制器中我这样调用：$this->pinyin1('这是中文字符串');

报错为：
ErrorException
iconv(): Detected an illegal character in input string

我在项目根目录下（与pulice并级）新建test.php调用这个拼音函数是能正确打印的。
这个问题出在哪，怎么解决？

//拼音函数

function getfirstchar($s0){
$fchar = ord($s0{0});
if($fchar >= ord("A") and $fchar <= ord("z") )return strtoupper($s0{0});
$s1 = iconv("UTF-8","gb2312", $s0);
$s2 = iconv("gb2312","UTF-8", $s1);
if($s2 == $s0){$s = $s1;}else{$s = $s0;}
$asc = ord($s{0}) * 256 + ord($s{1}) - 65536;
if($asc >= -20319 and $asc <= -20284) return "A";
if($asc >= -20283 and $asc <= -19776) return "B";
if($asc >= -19775 and $asc <= -19219) return "C";
if($asc >= -19218 and $asc <= -18711) return "D";
if($asc >= -18710 and $asc <= -18527) return "E";
if($asc >= -18526 and $asc <= -18240) return "F";
if($asc >= -18239 and $asc <= -17923) return "G";
if($asc >= -17922 and $asc <= -17418) return "H";
if($asc >= -17417 and $asc <= -16475) return "J";
if($asc >= -16474 and $asc <= -16213) return "K";
if($asc >= -16212 and $asc <= -15641) return "L";
if($asc >= -15640 and $asc <= -15166) return "M";
if($asc >= -15165 and $asc <= -14923) return "N";
if($asc >= -14922 and $asc <= -14915) return "O";
if($asc >= -14914 and $asc <= -14631) return "P";
if($asc >= -14630 and $asc <= -14150) return "Q";
if($asc >= -14149 and $asc <= -14091) return "R";
if($asc >= -14090 and $asc <= -13319) return "S";
if($asc >= -13318 and $asc <= -12839) return "T";
if($asc >= -12838 and $asc <= -12557) return "W";
if($asc >= -12556 and $asc <= -11848) return "X";
if($asc >= -11847 and $asc <= -11056) return "Y";
if($asc >= -11055 and $asc <= -10247) return "Z";
return null;
}

function pinyin1($zh){
$ret = "";
$s1 = iconv("UTF-8","gb2312", $zh);
$s2 = iconv("gb2312","UTF-8", $s1);
if($s2 == $zh){$zh = $s1;}
for($i = 0; $i < strlen($zh); $i++){
$s1 = substr($zh,$i,1);
$p = ord($s1);
if($p > 160){
$s2 = substr($zh,$i++,2);
$ret .= $this->getfirstchar($s2);
}else{
$ret .= $s1;
}
}
return $ret;
}