<?= $form->field($model,'city')->label(false)->widget(yiijuiAutoComplete::className(),[
    'clientOptions' => [
        'source' => ArrayHelper::getColumn(appmodelsCity::find()->select('city_name_ru')->all(),'city_name_ru'),
    ],
    'options' => [
        'class' => 'form-control',
        'placeholder' => 'Город',
        'value' => $city
    ]
])?>

appmodelsCity::find()->select('city_name_ru')->limit(100)->all();