public function actionUploadLogo(){
        $uploaded = UploadedFile::getInstance(new UploadLogo(),'logo');
         return $uploaded //a quick check here is null

        $uploaded->saveAs('uploads/settings/' . $uploaded->baseName
          . '.' . $uploaded->extension); //throws an error $uploaded is null

    }

class UploadLogo extends Model
{
public $logo;

public function rules()
{
    return [
        [['logo'], 'file', 'skipOnEmpty' => false, 'extensions' => 'png, jpg'],
    ];
}

public function upload()
{
    if ($this->validate()) {
        $this->logo->saveAs('uploads/settings/' . $this->logo->baseName . '.' . $this->logo->extension);
        return true;
    } else {
        var_dump($this->getErrors());
        die();
        return false;
    }
}
}

Array
(
 [logo] => Array
    (
        [name] => TWICE1.png
        [type] => image/png
        [tmp_name] => /tmp/phpj8dYFq
        [error] => 0
        [size] => 41646
    )

)

yiiwebUploadedFile Object
(
  [name] => TWICE1.png
  [tempName] => /tmp/php2JqCMw
  [type] => image/png
  [size] => 41646
  [error] => 0
 )