Optimization Of Fuel-saving Control Strategy For Hybrid Electric Vehicle Based On Energy Flow Test And Simulation

With the continuous improvement of China’s transportation network,cars as a fast means of transportation have been favored by more and more people.However,the industry’s swift expansion has caused environmental contamination and scarcity of oil resources.In order to deal with this problem,all over the world are constantly strengthening the research and development of hybrid electric vehicles(HEVs)and pure electric vehicles.In recent years,the research on HEVs has mainly focused on energy management and control strategies.In addition,the energy flow analysis of the whole vehicle as an effective research method is also widely used in the design and optimization of HEVs.Therefore,this thesis takes a HEV under the world light vehicle test cycle(WLTC)working condition as the research object.The rule-based control strategy and energy flow analysis method are used to study the impact of vehicle control strategy on fuel consumption of HEVs through Matlab/Simulink and GT-Suite simulation platform.Finally,the goal of reducing vehicle fuel consumption by more than 5% is achieved.The main research contents of this thesis include:(1)Energy flow test was carried out on the whole vehicle under WLTC working condition to obtain the working condition characteristics and energy flow characteristics of the whole vehicle.The test results showed that the low fuel consumption area of the engine was wide,and the motor torque and efficiency were relatively low in parallel mode,which provided guidance for the follow-up control strategy optimization research.(2)GT-Suite and Simulink were used to build the vehicle physical model and control model for HEV,respectively,and the test data of the WLTC working condition was used to complete the verification of the joint simulation model.The error between the measured and simulated data of the vehicle’s cumulative fuel consumption,power battery SOC,engine torque,motor torque,and generator speed was basically within 5%.This joint simulation model can be used for subsequent research.By using the method of energy flow analysis to simulate and analyze the HEV,it was found that the drive motor loss of the original vehicle was as high as 14%,mainly because many motor operating points were in the lower efficiency zone,and the energy loss of the reducer was also significant.In parallel mode,the engine charges the battery with the remaining energy output(24.3%)through the drive motor;In addition,the battery has a higher number of charges and discharges throughout the entire process.In the future,effective control strategies will be proposed to optimize these problems.(3)Through research on the control strategy of the HEV based on deterministic rules,it was found that the original vehicle uses the control strategy of six fixed working points of the engine to generate electricity in the series mode,and the engine works along the high and low SOC lines in the parallel mode.Through static calculation and analysis of the boundary of the series and parallel modes,the optimal steady-state working point of the series mode and the switching boundary of the series and parallel modes were determined.The efficiency,power generation and power consumption in series mode were controlled by adjusting the minimum power of the ranger.In parallel mode,the lower limit of cut-in parallel,the upper and lower limit of engine direct drive,and the limit of parallel charging torque were adjusted.Finally,combined with the series-parallel optimization direction,the optimization direction of the whole vehicle’s WLTC working condition was proposed,so as to obtain the relative optimal fuel consumption under the current architecture and configuration,providing the direction for the actual control strategy optimization.(4)Two different control strategy optimization schemes were proposed by analyzing the test data of the whole vehicle’s WLTC working condition,the distribution of the whole vehicle’s energy flow and the boundary of the series and parallel modes.The two schemes mainly adjusted the range of parallel torque,the speed threshold of series-parallel switching,and the switching conditions in parallel mode,and added the engine direct-drive mode in parallel mode.The two schemes were simulated by the verified simulation model,and the simulation results of the optimized scheme were analyzed in detail.(5)The optimization results showed that the two control strategy optimization schemes proposed in this thesis have reduced the fuel consumption of the HEV per 100 kilometers under WLTC conditions from 5.73 L/100 km to 5.37 L/100 km and 5.36 L/100 km,respectively,which were reduced by 6.3% and 6.5%,respectively.The two proposed schemes both meet the optimization target requirements.In scheme 1 and scheme 2,the proportion of energy used by the engine to drive the vehicle directly increased from 48.1%to 67.3% and 59.9%,respectively.The total energy loss of the vehicle powertrain system in Scheme 1 and Scheme 2 decreased from 30.6% to 21.1% and 22.4%,respectively.The powertrain system efficiencies of the original car,scheme 1 and scheme 2 were 88.14%,93.42% and 93.72%,respectively.This is the main reason for the reduction of fuel consumption under the control strategies of scheme 1 and scheme 2.Although the engine of the original car has the highest thermal efficiency,the entire powertrain system has the lowest efficiency and the highest fuel consumption.After optimizing the control strategy,it is found that the relative balance of the operating conditions of the engine,drive motor,generator and other power system components can reduce the fuel consumption of the vehicle.