\CModule::IncludeModule('bizproc');
$arParams = array(
    'param1' => 123,
    'param2' => 124,
    'TargetUser' => 'user_101',
);
\CBPDocument::StartWorkflow(
    $templateId,
    array("lists", "Bitrix\Lists\BizprocDocumentLists", $elementId),
    $arParams,
    $arErrorsTmp
);
if ($arErrorsTmp) {
    $message = '';
    foreach ($arErrorsTmp as $e) {
         $message .= $e['message'] . PHP_EOL;
    }
    self::log($message);
}