Research On Energy Management Strategies Of Extended Range Fuel Cell Electric Vehicles

Fuel cell vehicles are the development direction of new energy vehicles in the future for the advantages of low noise,no pollution,and high efficiency.However,fuel cells still have some shortcomings,such as slow cold start,slow dynamic response,and inability to recover electrical energy.In order to make up for these shortcomings,fuel cells are normally combined with other power sources to form a composite power system,giving full play to the respective advantages of the power sources to realize the recovery of braking energy,while improving the efficiency of power sources and the life of power systems.The research object of this article is a range-extended fuel cell electric vehicle,with fuel cells as the main power source and lithium batteries as an auxiliary energy source.Both rule-based and optimization-based energy management strategies are adopted.Energy management strategies are optimized for aspects such as hydrogen consumption,frequent start-stops,power efficiency,and power life degradation.First,the topological selection of the fuel cell composite power system is carried out,and the parameters of the power supply device are matched according to the dynamic indicators such as climbing,acceleration,maximum speed and cruising range indicators.With reference to a fuel cell electric vehicle,a longitudinal dynamic model of the vehicle is established.Based on the simplified circuit of lithium battery,fuel cell and DC converter,a composite power system model is built,which mainly includes the output voltage model and charge calculation model of lithium battery,the hydrogen consumption model and output voltage model of fuel cell,and the DC converter model.Then,rule-based energy management strategies are established.A state machine strategy and a fuzzy logic-based energy management strategy are designed,and the two strategies are both improved.The start-stop strategy of the fuel cell system is added to the state machine strategy to satisfy the energy distribution and reduce the number of start-stop times of the fuel cell system.The efficiency of the fuel cell system is considered in the fuzzy logic strategy.The efficiency of the fuel cell system is divided into different regions,and improved fuzzy rules are formulated.The results show that: the improved fuzzy logic strategy improves the efficiency of the power system and reduces the hydrogen consumption.Finally,optimization-based energy management strategies are established.Based on the equivalent hydrogen consumption minimum strategy,the effects of start-stop conditions,high and low load conditions,and transient conditions on the service life of the fuel cell are considered separately.Then the life cost minimum strategy is proposed and optimization objective function and constraints are set up.Then the four strategies are simulated and analyzed under the world light vehicle test procedure and China’s typical urban driving cycle.The system efficiency,hydrogen consumption level,loss cost and other indicators are compared.The results show that: the transient operating conditions and high and low current operating conditions have a greater degradation of the power system,and the formulated life cost minimum strategy achieves better hydrogen consumption economy and can effectively improve the fuel cell life level.