How to upload image in the yii2 - yii2

Question

I have one problem in yii2 when I use
$model = Client::find()->where('id=1')->one();
UploadedFile::getInstance($model, 'logo');
then this gitme NULL value. Why am I getting NULL if I print $_FILES and them I see the array values.
I have use the simple upload file in yii2
My view :
$form = ActiveForm::begin(['action' => ['center/updatelogo'], 'layout' => 'horizontal', 'options' => ['enctype' => 'multipart/form-data']]);
echo $form->field($model, 'logo')->widget(FileInput::classname(), [
'options' => ['accept' => $model->logo, 'class' => 'form-control'],
'pluginOptions' => [
'allowedFileExtensions' => ['png', 'jpg'],
'maxFileSize' => 25000,
],
]);
My controller:
$model = Client::find()->where('id=1')->one();
if (Yii::$app->request->isPost) {
$model->file = UploadedFile::getInstance($model, 'logo');
if ($model->validate()) {
$model->file->saveAs('logos/' . $model->file->baseName . '.' . $model->file->extension);
}
}
var_dump($file);die();
I need upload one file to mi server and put the logo, what happened?
my $_POST and my $_FILES :
array(2) {
["_csrf"]=>
string(88) "WF67odQ_DUylcUprRN9FssjEdq5nBn2ARrjjql_D8af6Y1am1ID7AEG5KV2iWNL-7QeEoeGF_UJQYxnH6JgS1A=="
["Center"]=>
array(1) {
["logo"]=>
string(0) ""
}
}
array(1) {
["Center"]=>
array(5) {
["name"]=>
array(1) {
["logo"]=>
string(19) "Libre Albedrío.jpg"
}
["type"]=>
array(1) {
["logo"]=>
string(10) "image/jpeg"
}
["tmp_name"]=>
array(1) {
["logo"]=>
string(14) "/tmp/phpYijyXv"
}
["error"]=>
array(1) {
["logo"]=>
int(0)
}
["size"]=>
array(1) {
["logo"]=>
int(19900)
}
}
}