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基于聚类优化等效因子的分布式混动拖拉机能量管理策略

Energy management strategy for distributed hybrid electric tractors based on clustering optimization equivalent factors

  • 摘要: 分布式混合动力拖拉机(distributed hybrid electric tractor, DHET)多动力源解耦特性显著提升了系统能效与工况适应潜力,同时也对动态工况下的能量分配效率提出了更高要求。自适应等效最小燃油算法(adaptive equivalent consumption minimization strategy, A-ECMS)因具有较好的燃油经济性和可优化潜力被广泛应用于混动系统的能量管理问题,但其优化效果过于依赖等效因子的动态标定精度,因此,该研究针对现有自适应等效最小燃油算法中等效因子实时优化在工况性适应性方面的不足,提出一种融合聚类优化与A-ECMS的能量管理策略,采用分层架构通过多阶段优化提升策略的工况适应性和燃油经济性。首先,针对传统工况划分主观性较强的问题,通过K-means聚类算法对标准工况进行聚类分析,并引入轮廓系数(silhoiette coefficient, SC)作为聚类有效性评价指标,确定最佳簇类数量;针对聚类结果,采用动态规划算法(dynamic programming, DP)求解不同簇类的最优等效因子;其次,为解决在线控制中单一等效因子的适应性缺陷,构建了基于连续权重重核函数的等效因子映射模型,基于实时工况特征与离线聚类中心动态匹配等效因子,实现等效最小燃油算法的自适应调整。硬件在环结果表明,该方法能够在绝大部分工况下维持发动机和电机工作在高效区间,在测试工况下,等效燃油消耗量相较于基于PI控制器的自适应等效最小燃油算法降低了6.54%,有效提升了混合动力拖拉机燃油经济性。

     

    Abstract: A tractor is one of the most important power equipment in sustainable agriculture. Complex and variable field conditions can often lead to frequent fluctuations in traction resistance during plowing. It is often required to maintain the highly efficient and energy-saving operation. The conventional tractors with the internal combustion engine are restricted to carbon emissions and thermal efficiency. Alternatively, the pure electric solutions are also limited by current battery technology, in terms of the energy density and endurance. An adaptive equivalent consumption minimization strategy (A-ECMS) has been widely used in hybrid power systems due to its excellent fuel economy and optimization potential. The energy management strategy can directly dominate the overall performance of the vehicle. The high efficiency, energy savings, and reliable operation can be expected for the hybrid electric tractors. However, the effectiveness of this algorithm can highly depend on the dynamic calibration accuracy of the equivalent factor, which can suffer from the limited adaptability under varying working conditions. In this study, a distributed hybrid electric tractor (DHET) architecture was proposed with a decoupled power output, in order to fully meet the demands of the high-power continuous operation. The energy efficiency and operational adaptability were significantly improved to decouple the multiple power sources, in order to fully meet the higher requirements on the efficiency of the energy allocation under dynamic working conditions. Therefore, an energy management strategy was proposed to integrate the clustering optimization and A-ECMS. A hierarchical architecture was adopted to enhance the adaptability and fuel economy of the control strategy after the multi-stage optimization. Specifically, a K-means clustering algorithm was introduced to analyze the standard cycles in the conventional working condition division. The silhouette coefficient (SC) was also used as an evaluation metric in order to determine the optimal number of clusters. Furthermore, the dynamic programming (DP) was then employed to solve for the optimal equivalent factor corresponding to each cluster. A mapping model of the equivalent factor was constructed to compare the single equivalent factor in online control, according to a continuous weight re-kernel function. The equivalent factor was matched dynamically, according to the real-time features of the working condition and offline cluster centers, thereby enhancing the adaptive adjustment of the A-ECMS algorithm. Hardware-in-the-loop (HIL) experiments demonstrated that the engine and motor operation were maintained within the high-efficiency ranges under most working conditions. Under the tested conditions,the proportion of operating points within the high-efficiency range for the engineincreased by 4.40%, while the proportion in the low-efficiency range decreased by 10.21%. For the motor, the proportion ofoperating points within the high-efficiency range increased by 4.28%, and the proportion in the low-efficiency range decreasedby 1.20%. The equivalent fuel consumption of this strategy was reduced by 6.54% under the tested conditions, compared with the adaptive equivalent consumption minimization using a PI controller. Therefore, the fuel economy of the hybrid electric tractor was significantly improved for the promising prospects in the engineering applications.

     

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