您可以像下面这样获得这个参数：

You can get this param like below:

public function actionChargesCash($id,$room_category){
    $model = \app\models\IpdCharges::findOne(['id'=>$id,'room_category'=>$room_category]);
    //rest of code
}

还有另一种方法可以做到这一点：

There is another way to do that:

public function actionChargesCash($id){
    $room_category=Yii::$app->getRequest()->getQueryParam('room_category');
    $model = \app\models\IpdCharges::findOne(['id'=>$id,'room_category'=>$room_category]);
    //rest of code
}