An Improved Gated Recurrent Unit Network Model for State-of-Charge Estimation of Lithium-Ion Battery
Abstract
:1. Introduction
1.1. Literature Review
1.2. The Contributions
- (1)
- Deep learning technology can solve the problem of low prediction accuracy of battery SOC by a traditional neural network. This technology does not need to establish an accurate battery equivalent circuit model. It can simplify the tedious parameter adjustment process based on the model method, and greatly save the time needed in the whole process of SOC estimation;
- (2)
- Compared with an LSTM network, a GRU network structure has the advantages of fewer parameters and a simple structure. It can save a lot of training and prediction time on the premise of ensuring the prediction accuracy of the model. Compared with FNN, LSTM, and GRU network models, it was found that the proposed model can obtain more accurate and stable SOC estimation results in different operating conditions. The Tanh activation function is a saturated activation function, which can enhance the nonlinear learning ability of neural network. The leaky ReLU and the clipped ReLU are unsaturated activation functions, which can solve the problem of gradient disappearance encountered in the neural network. The output of the neural network was limited to a certain area, which improved the prediction performance of the model. Adding the above three activation function layers in the GRU-RNN network can improve the prediction accuracy and robustness of the model;
- (3)
- The SOC prediction performance of LSTM, GRU, and GRU-ATL network models was compared when the measurement signals contain Gaussian noise and non-Gaussian noise. The experimental results showed that the SOC prediction accuracy of GRU-ATL model was 0.1–0.4% higher than GRU model and 0.3–0.7% higher than LSTM model;
- (4)
- The battery model obtained by the deep learning network can be used for SOC online prediction in different temperature working conditions. The GRU-ATL model still had high prediction accuracy and robustness when the measurement data contains noise. Therefore, it could meet the complex dynamic conditions of vehicles.
1.3. The Organization of the Paper
2. GRU-FC Network Model
2.1. GRU Structural Unit
2.2. SOC Estimation Based on GRU-ATL Network
2.3. Selection of Other Parameters in Network
3. Battery Data Description and Processing Process
3.1. Battery Data Description
3.2. Data Processing Process and Evaluation Indicators
4. Experimental Results and Discussion
4.1. SOC Estimation Results of Four Network Models
4.2. SOC Estimation Results under Unknown Conditions
4.3. SOC Estimation Results with Noise
5. Conclusions
- (1)
- Compared with an LSTM network, a GRU network structure has the advantages of fewer parameters and simple structure. It can save a lot of training and prediction time on the premise of ensuring the prediction accuracy of the model. Compared with FNN, LSTM, and GRU network models, it was found that the proposed model could obtain more accurate and stable SOC estimation results in different operating conditions. Adding the above three activation function layers in the GRU-RNN network could improve the prediction accuracy and robustness of the model;
- (2)
- The prediction accuracy of the model could be improved by appropriately increasing the number of neurons in the GRU layer and FC layer. But the excessive number of neurons in the two layers caused an over fitting phenomenon, which affected the SOC estimation accuracy. In order to save computation, the number of neurons in the GRU layer was 2–3 times less than that in the FC layer. A large number of experiments showed that the SOC was more accurate when the number of neurons in the GRU layer was 55 and that of the FC layer was 160. The MAE was less than 1.3% and RMSE was less than 2%;
- (3)
- The SOC prediction performance of LSTM, GRU, and GRU-ATL network models was compared when the measurement signals contained Gaussian noise and non-Gaussian noise. The experimental results showed that the SOC prediction accuracy of GRU-ATL model was 0.1–0.4% higher than the GRU model and 0.3–0.7% higher than the LSTM model. The MAE of SOC predicted by the GRU-ATL model was stable in the range of 0.7–1.4%, and the RMSE was stable between 1.2–1.9%. The SOC prediction results of the GRU-ATL network model were still more accurate and stable at a low temperature;
- (4)
- The experiments in this paper showed that the GRU-ATL network model could realize online SOC estimation under different working conditions without relying on an accurate battery model. When the measurement data contained noise, the model still had high prediction accuracy and robustness, which could meet the SOC estimation in complex vehicle working conditions.
Author Contributions
Funding
Conflicts of Interest
References
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Parameter | Value |
---|---|
Nominal capacity/voltage | 3.0 Ah/3.6 V |
Charge and discharge cut-off voltage | 4.2 V/2.5 V |
Normal end-of-charge current | 50 mA |
Max continuous discharge current | 20 A |
Standard charge current | 1.5 A |
Energy density | 240 Wh/Kg |
Data Set | T (°C) | Condition |
---|---|---|
Training | −10, 0, 10, 25, 40 | Mixed (1–8), CC-CV (3A), UDDS, HWFET, LA92, US06 |
Testing 1 | −10 | UDDS, HWFET, LA92, US06, CC-CV (3A) |
Testing 2 | 0 | UDDS, HWFET, LA92, US06, CC-CV (3A) |
Testing 3 | 10 | UDDS, HWFET, LA92, US06, CC-CV (3A) |
Testing 4 | 25 | UDDS, LA92, US06, CC-CV (3A) |
Testing 5 | 40 | UDDS, HWFET, LA92, US06, CC-CV (3A) |
Network Model | T (°C) | UDDS | LA92 | US06 | CC-CV | ||||
---|---|---|---|---|---|---|---|---|---|
MAE (%) | RMSE (%) | MAE (%) | RMSE (%) | MAE (%) | RMSE (%) | MAE (%) | RMSE (%) | ||
FNN | −10 | 5.303 | 6.489 | 4.869 | 6.594 | 9.066 | 11.899 | 11.479 | 14.352 |
0 | 4.041 | 4.821 | 3.437 | 4.507 | 7.519 | 9.632 | 9.475 | 11.597 | |
10 | 2.726 | 3.328 | 2.451 | 3.216 | 6.037 | 7.680 | 8.139 | 10.425 | |
25 | 1.612 | 2.078 | 1.784 | 2.404 | 4.305 | 5.490 | 7.427 | 8.827 | |
40 | 1.517 | 1.920 | 1.615 | 2.105 | 3.363 | 4.289 | 7.808 | 9.438 | |
LSTM | −10 | 2.067 | 2.993 | 1.658 | 2.085 | 2.265 | 2.77 | 2.075 | 2.822 |
0 | 1.256 | 2.471 | 1.271 | 1.613 | 2.216 | 2.834 | 2.868 | 3.313 | |
10 | 1.572 | 2.264 | 1.227 | 1.605 | 2.297 | 2.954 | 1.714 | 1.999 | |
25 | 1.261 | 2.017 | 1.080 | 1.416 | 2.225 | 2.787 | 2.869 | 3.249 | |
40 | 1.327 | 2.103 | 1.164 | 1.489 | 1.870 | 2.286 | 2.068 | 2.389 | |
GRU | −10 | 0.558 | 0.899 | 0.454 | 0.551 | 1.587 | 1.724 | 3.165 | 4.387 |
0 | 1.129 | 2.333 | 0.694 | 0.865 | 1.294 | 1.670 | 1.650 | 2.069 | |
10 | 0.702 | 1.314 | 0.461 | 0.554 | 1.474 | 1.842 | 1.409 | 1.901 | |
25 | 0.988 | 1.454 | 0.570 | 0.714 | 1.007 | 1.253 | 1.847 | 2.179 | |
40 | 0.612 | 1.046 | 0.620 | 0.800 | 0.989 | 1.321 | 1.604 | 2.072 | |
GRU-ATL | −10 | 0.424 | 0.752 | 0.445 | 0.596 | 1.126 | 1.323 | 2.436 | 3.004 |
0 | 0.406 | 1.161 | 0.361 | 0.500 | 1.324 | 1.898 | 1.142 | 1.685 | |
10 | 0.457 | 0.859 | 0.638 | 0.765 | 1.429 | 1.730 | 0.799 | 1.066 | |
25 | 0.814 | 1.165 | 0.526 | 0.652 | 0.978 | 1.179 | 1.407 | 1.763 | |
40 | 0.609 | 0.890 | 0.541 | 0.709 | 0.911 | 1.148 | 1.303 | 1.613 |
Case 1 | NFC | 10 | 30 | 70 | 100 | 130 | 160 | 200 | 230 | 260 | 300 |
MAE (%) | 0.956 | 0.832 | 1.113 | 0.775 | 0.787 | 0.734 | 1.094 | 0.949 | 1.032 | 1.179 | |
RMSE (%) | 1.623 | 1.628 | 1.812 | 1.347 | 1.291 | 1.158 | 1.779 | 1.556 | 1.623 | 1.544 | |
Time (h) | 5.92 | 5.95 | 6.01 | 6.03 | 6.13 | 6.15 | 6.18 | 6.21 | 6.26 | 6.33 | |
Case 2 | NGRU | 10 | 30 | 70 | 100 | 130 | 160 | 200 | 230 | 260 | 295 |
MAE (%) | 1.283 | 0.988 | 0.979 | 0.911 | 0.840 | 1.029 | NA | 0.997 | NA | 1.093 | |
RMSE (%) | 2.056 | 1.543 | 1.433 | 1.555 | 1.311 | 1.338 | NA | 1.636 | NA | 1.575 | |
Time (h) | 4.37 | 4.98 | 7.05 | 10.26 | 15.55 | 22.38 | NA | 28.93 | NA | 34.16 | |
Case 3 | NGRU and NFC | 10 | 30 | 70 | 100 | 130 | 160 | 200 | 230 | 260 | 300 |
MAE (%) | 1.095 | 0.854 | 0.831 | 0.945 | 1.014 | 1.096 | 0.934 | NA | 0.930 | 1.083 | |
RMSE (%) | 1.969 | 1.845 | 1.482 | 1.466 | 1.678 | 1.571 | 1.553 | NA | 1.329 | 1.565 | |
Time (h) | 4.27 | 5.01 | 8.36 | 12.37 | 17.52 | 21.05 | 24.37 | NA | 30.45 | 35.25 |
T (°C) | −10 | 0 | 10 | 25 | 40 |
---|---|---|---|---|---|
MAE (%) | 1.271 | 0.814 | 1.032 | 0.734 | 0.799 |
RMSE (%) | 2.005 | 1.101 | 1.461 | 1.158 | 1.259 |
Network Model | Noise 1 | Noise 3 | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
T (°C) | −10 | 0 | 10 | 25 | 40 | −10 | 0 | 10 | 25 | 40 | ||
LSTM | Case 1 | MAE (%) | 1.755 | 1.293 | 1.202 | 1.195 | 1.157 | 1.738 | 1.306 | 1.197 | 1.201 | 1.160 |
RMSE (%) | 2.369 | 1.879 | 1.695 | 1.751 | 1.689 | 2.358 | 1.894 | 1.693 | 1.754 | 1.691 | ||
Case 2 | MAE (%) | 1.820 | 1.364 | 1.295 | 1.288 | 1.258 | 1.738 | 1.357 | 1.457 | 1.284 | 1.284 | |
RMSE (%) | 2.449 | 1.943 | 1.815 | 1.195 | 1.782 | 2.669 | 1.878 | 1.962 | 1.853 | 1.813 | ||
Case 3 | MAE (%) | 1.756 | 1.301 | 1.206 | 1.198 | 1.161 | 1.750 | 1.317 | 1.210 | 1.201 | 1.168 | |
RMSE (%) | 2.370 | 1.886 | 1.699 | 1.753 | 1.692 | 2.372 | 1.911 | 1.704 | 1.755 | 1.670 | ||
Case 4 | MAE (%) | 1.788 | 1.335 | 1.265 | 1.266 | 1.234 | 1.981 | 1.317 | 1.414 | 1.251 | 1.255 | |
RMSE (%) | 2.410 | 1.915 | 1.780 | 1.815 | 1.759 | 2.572 | 1.850 | 1.913 | 1.823 | 1.786 | ||
GRU | Case 1 | MAE (%) | 1.687 | 1.277 | 1.169 | 1.272 | 1.010 | 1.687 | 1.295 | 1.165 | 1.281 | 1.015 |
RMSE (%) | 2.440 | 1.808 | 1.610 | 1.826 | 1.411 | 2.441 | 1.828 | 1.608 | 1.835 | 1.417 | ||
Case 2 | MAE (%) | 1.697 | 1.299 | 1.180 | 1.305 | 1.113 | 1.687 | 1.160 | 1.410 | 1.250 | 1.062 | |
RMSE (%) | 2.469 | 1.828 | 1.638 | 1.860 | 1.506 | 2.494 | 1661 | 1.832 | 1.805 | 1.439 | ||
Case 3 | MAE (%) | 1.692 | 1.278 | 1.169 | 1.272 | 1.011 | 1.700 | 1.297 | 1.168 | 1.273 | 1.019 | |
RMSE (%) | 2.449 | 1.808 | 1.611 | 1.827 | 1.411 | 2.450 | 1.829 | 1.609 | 1.825 | 1.421 | ||
Case 4 | MAE (%) | 1.697 | 1.298 | 1.176 | 1.299 | 1.089 | 1.700 | 1.176 | 1.388 | 1.238 | 1.035 | |
RMSE (%) | 2.473 | 1.826 | 1.634 | 1.853 | 1.479 | 2.473 | 1.679 | 1.810 | 1.795 | 1.411 | ||
GRU-ATL | Case 1 | MAE (%) | 1.249 | 0.697 | 0.998 | 0.891 | 0.937 | 1.247 | 0.696 | 1.009 | 0.901 | 0.947 |
RMSE (%) | 1.859 | 1.155 | 1.409 | 1.248 | 1.273 | 1.863 | 1.159 | 1.422 | 1.257 | 1.282 | ||
Case 2 | MAE (%) | 1.265 | 0.718 | 1.038 | 0.924 | 1.055 | 1.247 | 0.887 | 0.909 | 0.828 | 0.906 | |
RMSE (%) | 1.888 | 1.171 | 1.45 | 1.288 | 1.413 | 1.865 | 1.235 | 1.278 | 1.197 | 1.275 | ||
Case 3 | MAE (%) | 1.251 | 0.698 | 1.002 | 0.893 | 0.940 | 1.264 | 0.705 | 1.010 | 0.890 | 0.960 | |
RMSE (%) | 1.864 | 1.158 | 1.413 | 1.250 | 1.278 | 1.878 | 1.175 | 1.422 | 1.247 | 1.294 | ||
Case 4 | MAE (%) | 1.268 | 0.722 | 1.040 | 0.928 | 1.042 | 1.359 | 0.855 | 0.910 | 0.828 | 0.893 | |
RMSE (%) | 1.892 | 1.176 | 1.450 | 1.292 | 1.395 | 1.865 | 1.218 | 1.281 | 1.195 | 1.259 |
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Duan, W.; Song, C.; Peng, S.; Xiao, F.; Shao, Y.; Song, S. An Improved Gated Recurrent Unit Network Model for State-of-Charge Estimation of Lithium-Ion Battery. Energies 2020, 13, 6366. https://doi.org/10.3390/en13236366
Duan W, Song C, Peng S, Xiao F, Shao Y, Song S. An Improved Gated Recurrent Unit Network Model for State-of-Charge Estimation of Lithium-Ion Battery. Energies. 2020; 13(23):6366. https://doi.org/10.3390/en13236366
Chicago/Turabian StyleDuan, Wenxian, Chuanxue Song, Silun Peng, Feng Xiao, Yulong Shao, and Shixin Song. 2020. "An Improved Gated Recurrent Unit Network Model for State-of-Charge Estimation of Lithium-Ion Battery" Energies 13, no. 23: 6366. https://doi.org/10.3390/en13236366