Abstract

Nonlinear system prediction plays an important role in the practical thermal process, and deep learning algorithm is now popular in nonlinear dynamic system modeling because of its powerful learning ability. In this paper, the dynamic artificial neural networks (DANNs), which can be divided into two different types with external dynamic characteristics and internal dynamic characteristics, are analyzed. The mathematical formulations of feedforward deep neural network (DNN), traditional recurrent neural network (RNN) and Long-Short Term Memory network (LSTM) models are given. Furthermore, the structure of deep Hybrid Neural Network (DHNN) is described. Finally, the applicability of the above models in the thermal nonlinear process with different structural features is discussed. Simulation experiments reveal that DANNs with internal dynamic characteristics more suitable for solving thermal nonlinear system modeling problems with unknown order, and DHNN based on LSTM model has performed much better in approximating the dynamics of the thermal process with state parameters.

Highlights

  • Recent years, system modeling has made great progress due to the huge demand for controller design, and process analysis [1, 2]

  • System prediction for nonlinear system usually has developed by focusing on specific classes of system and can be broadly categorized into five basic description approaches, each defined by a model class: Volterra series models [5], block structured models, neural network models [6], NARMAX models [7], State-space models [8]

  • We apply deep neural network (DNN), recurrent neural network (RNN), Long-Short Term Memory network (LSTM) and deep Hybrid Neural Network (DHNN) based on LSTM models to thermal nonlinear dynamic prediction and compare the prediction ability of the above models in two situations: one is nonlinear dynamic objects with known order, the other is unknown input and output parameter order

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Summary

Introduction

System modeling has made great progress due to the huge demand for controller design, and process analysis [1, 2]. Compared with FFNN's difficulty, the neural network which include the dynamics directly into its structure can learn the dynamics of the system without requiring any apriori knowledge regarding the system. These neural networks with self-feedback loops are called RNN. The deep hybrid neural network based on DNN and RNNs is rarely applied in thermal nonlinear dynamic processes modeling/ identification. We apply DNN, RNN, LSTM and DHNN based on LSTM models to thermal nonlinear dynamic prediction and compare the prediction ability of the above models in two situations: one is nonlinear dynamic objects with known order, the other is unknown input and output parameter order. A brief mathematical theory of the deep neural networks which can represent the above types is introduced

DNN model
RNN model
LSTM model
Applicability of deep learning in thermal nonlinear system
Application of conventional deep neural network
Application of deep Hybrid neural network
Simulation study
Example 1
Discussion on the training simulation results
Discussion on the testing simulation results
Example 2
Discussion on DNN based simulation results
Conclusions

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