import tensorflow as tf
import tf2onnx
import onnx
input_signature = [tf.TensorSpec([1, 3, 640, 640], tf.float32, name="data")]
frozen_path = 'your_model.pb'
model = MobilenetV2(frozen_path)
onnx_model, _ = tf2onnx.convert.from_keras(model, input_signature, opset=13)
onnx.save(onnx_model, "your_model.onnx")