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Journal of ZheJiang University (Engineering Science)  2023, Vol. 57 Issue (10): 2051-2059    DOI: 10.3785/j.issn.1008-973X.2023.10.014
    
Seq2Seq prediction method of state of charge of electric bus battery
Hong-zhao DONG(),Zhen WANG,Nan ZHANG,Yi-ni SHE,Ying-ying LIN
Joint Institute of Intelligent Transportation System, College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
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Abstract  

A Seq2Seq prediction method for the state of charge of electric bus batteries was proposed to address the difficulty of predicting the state of charge under high-dimensional input features and long-term prediction needs. The battery state prediction was enhanced by incorporating vehicle driving status and operating conditions. The impact of various factors on the state of charge was analyzed using feature selection algorithms. The WN-Seq2Seq algorithm integrated Seq2Seq and WaveNet cyclic structures, which could enhance the memory and representation ability of high-dimensional input features and predicted state of charge sequence information. The accuracy of the model's prediction was improved. Validation using actual driving data from four electric buses in Hangzhou from 2021 to 2022 demonstrated the effectiveness of the WN-Seq2Seq model. The mean squared error (MSE) reached 0.505%, the mean absolute error (MAE) reached 0.479%, the mean absolute percentage error (MAPE) reached 0.656%, and the model computation time (MCT) reached 0.017 s. The prediction accuracy and stability were significantly promoted compared with traditional models. The WN-Seq2Seq model exhibited good prediction performance across different temperature ranges. The findings provide reliable decision-making support for energy consumption control strategies and safety management of electric buses.



Key wordselectric bus      state of charge prediction      deep learning      sequence to sequence      recurrent neural networks     
Received: 06 November 2022      Published: 18 October 2023
CLC:  TM 912  
Fund:  国家自然科学基金资助项目(61773347);浙江省公益技术研究项目(LGF20F030001)
Cite this article:

Hong-zhao DONG,Zhen WANG,Nan ZHANG,Yi-ni SHE,Ying-ying LIN. Seq2Seq prediction method of state of charge of electric bus battery. Journal of ZheJiang University (Engineering Science), 2023, 57(10): 2051-2059.

URL:

https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2023.10.014     OR     https://www.zjujournals.com/eng/Y2023/V57/I10/2051


电动公交车电池荷电状态的Seq2Seq预测方法

针对高维输入特征和长时预测需求下荷电状态预测困难的问题,提出一种电动公交车电池荷电状态的Seq2Seq预测方法. 在电池状态的基础上引入车辆行驶状态和行驶工况,利用特征选择算法分析各因素对荷电状态的影响. 以LSTM为基本单元结构,WN-Seq2Seq算法融合Seq2Seq与WaveNet循环结构,可以强化高维输入特征与预测荷电状态的序列信息记忆与表征能力,从而提高模型的预测精度. 通过2021—2022年杭州市4辆电动公交车实际行驶数据验证表明,在引入车辆行驶状态和行驶工况后,WN-Seq2Seq模型的评价指标均方误差(MSE)、平均绝对误差(MAE)、平均绝对百分比误差(MAPE)和模型计算时间(MCT)分别为0.505%、0.479%、0.656%和0.017 s. 研究结果表明相比传统模型,预测精度及稳定性都有所提升,在不同温度区间下都具有良好的预测效果,为电动公交车能耗控制策略、安全管理提供合理且可靠的参数决策支持.


关键词: 电动公交车,  荷电状态预测,  深度学习,  序列到序列,  循环神经网络 
数据名称 数值
采样时间 2021?03?22 12:29:58
经度/(°) 120.113 67
纬度/(°) 30.296 56
车速/(km·h?1) 11.796 875
电机转速/(r·min?1) 1 435.0
总行驶里程/km 113 709.3
电池组总电流/A 289.6
电池组总电压/V 494.0
电池组平均温度/℃ 21.5
SOC/% 69.8
Tab.1 Actual driving data sample of electric bus
类型 特征名称
电池状态 SOC/%
电池组总电压/V
电池组总电流/A
电池组平均温度/℃
车辆行驶状态 车速/(km·h?1)
电机转速/(r·min?1)
总行驶里程/km
经度/(°)
纬度/(°)
行驶工况 平均加速度/(m·s?1)
平均减速度/(m·s?1)
平均速度/(m·s?1)
行驶里程/km
行驶时间/s
Tab.2 Influence factor characteristic of electric bus battery SOC
Fig.1 Importance degree of SOC features
特征分类 输入特征
电池状态 SOC/%
电池组总电压/V
电池组总电流/A
电池组平均温度/℃
车辆行驶状态 车速/(km·h?1)
总行驶里程/km
行驶工况 平均加速度/(m·s?1)
平均减速度/(m·s?1)
Tab.3 Input features of SOC prediction models
Fig.2 Encoder-decoder model structure of Seq2Seq
Fig.3 Encoder-decoder model structure of WN-Seq2Seq
Fig.4 Diagram of in decoder LSTM unit structure
Fig.5 LSTM unit structure diagram in decoder
隐层状态维度 MSE/% MAE/% MAPE/%
32 0.609 0.575 0.765
64 0.505 0.479 0.656
128 0.508 0.484 0.663
Tab.4 Evaluation of WN-Seq2Seq prediction results for different hidden state dimensions
模型名称 MSE/% MAE/% MAPE/% MCT/s
LSTM 1.163 0.709 0.960 0.001
BILSTM 1.090 0.657 0.886 0.002
Seq2Seq 0.698 0.549 0.757 0.012
WN-Seq2Seq 0.505 0.479 0.656 0.017
Tab.5 Evaluation of prediction results and calculation time of each model
Fig.6 Comparison of SOC curves and errors predicted by different models
特征类别 MSE/% MAE/% MAPE/% MCT/s 特征类别 MSE/% MAE/% MAPE/% MCT/s
电池状态 0.683 0 0.599 0 0.817 0 0.014 5 电池状态+行驶工况 0.562 0 0.534 0 0.723 0 0.016 0
电池状态+车辆
行驶状态
0.546 0 0.529 0 0.721 0 0.014 9 电池状态+车辆行驶
状态+行驶工况
0.505 0 0.479 0 0.656 0 0.017 0
Tab.6 Evaluation of WN-Seq2Seq prediction results for different feature categories
Fig.7 Prediction curve and error of WN-Seq2Seq in single charge-discharge cycle
温度区间/℃ MSE/% MAE/% MAPE/%
0~10 0.489 0.464 0.709
10~20 0.549 0.499 0.659
20~30 0.524 0.496 0.588
30~40 0.469 0.461 0.687
Tab.7 Evaluation of WN-Seq2Seq prediction results in different temperature ranges
Fig.8 Comparison of WN-Seq2Seq predicted SOC curves in different temperature ranges
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