ZZCX_yii/backend/modules/api/api.php

<?php

namespace backend\modules\api;
use yii\base\Module;
/**
 * zzcs module definition class
 */
class api extends Module
{
    /**
     * @inheritdoc
     */
    public $controllerNamespace = 'backend\modules\api\controllers';

    /**
     * @inheritdoc
     */
    public function init()
    {
        define('APP_MODULES_PATH', __DIR__);
        parent::init();
        // custom initialization code goes here
    }
}