Optimal power management for the UTS plug-in hybrid electric vehicle
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There is a great potential for significant improvement to be made in energy efficiency and all-electric drive performance of the different types of existing powertrain architectures, such as: 1) traditional internal combustion engine (ICE) powered vehicles; 2) electric vehicles (EVs); 3) hybrid EVs (HEVs), which consist of three types according to the power flow: 1) series; 2) parallel; and 3) series-parallel; and 4) plug-in HEVs (PHEVs) through implementing innovative technologies. Many major car manufacturers have been making great efforts to develop an alternative form of transportation that can offer better solutions to reduce the serious undesirable impacts to the environment and economy. The new type of vehicles will win quick acceptance in the marketplace because of the current high fuel cost and greenhouse gas emissions. Today PHEV is more promising in energy efficiency than HEV s if the energy storage system (ESS) is recharged by electricity generated from dean energy sources, such as wind and solar. Most of the existing powertrain architectures need two electric machines (EMs) to function as an electric motor and generator respectively. To improve the vehicle all-electric drive performance and energy efficiency, the University of Technology, Sydney (UTS) PHEV is proposed, which is a series-parallel type. The UTS PHEV requires only a single EM in its powertrain to function as an electric motor or generator in different time intervals controlled by a special energy management strategy (EMS). This powertrain uses two electtic energy sources, which are battery and ultracapacitor packs that can work together to maintain the state of charge (SOC) at a high level in order to improve vehicle all-electric drive performance and energy efficiency. While the main drive power of the UTS PHEV comes from the electric motor supplied by the battery pack, the ICE is needed as a back-up and auxiliary power source. Adding the ultracapacitor pack to this powertrain can more effectively capture the regenerative braking energy resulting in better energy efficiency and meet large power demand from the electric motor, providing better dynamic drive performance and all electric range (AER). In comparison with the HEY s, the size of the ICE can be reduced since it is needed just as auxiliary drive when there is a need for extra power during fast acceleration or hill climbing and for battery charging when the SOC is low during long distance drives. In this work, through a power flow analysis of the powertrain, the vehicle main components were sized according to the vehicle parameters, specifications and perfonnance requiren1ents to meet the expected power requirements for steady state velocity of an average typical 5-passenger car. After the sizing process, the components were selected based on the parameters and specifications of each component. Then, the model of individual components that make up the overall structure of the UTS PHEV powertrain, known as UTS PHEV code are derived and implemented numerically in the MA TLAB/SIMULINK environment to study their operational performance in vanous drive cycles measured under real-life conditions. The accuracy of the model is verified and validated by a comparison between the simulation results from the UTS PHEV and the Advanced Vehicle Simulator (ADVISOR) codes during a number of standard drive cycles. The simulation results of the selected subsystems from both codes are compared and the advantages and disadvantages are discussed. Extensive analysis has been conducted on the fuel economy, emissions: 1) hydro carbon; 2) carbon monoxide; and 3) nitrogen oxides, electrical consumption, AER, operation cost and total lifetime cost computed for different standard drive cycles, developed low and high density traffic patterns drive cycles and example of high congestion drive cycle. The main objective of the test procedure design is to optimize the power and energy demands throughout the system and compare the fuel economy, emissions, electrical consumption, AER , operation cost and total lifetime cost of the UTS PHEV code with the existing powertrain architectures by satisfying the test procedure inputs. The power balance requirements between the battery and ultracapacitor packs in its ESS is also studied by testing the effectiveness of the developed EMS using the three different selected standard drive cycles. The optimization of a power flow management in the UTS PHEV powertrain v1a parametric study and genetic algorithn1 method of optimization is implemented in this work for several standard drive cycles. The objective of this optimization is to obtain the best design variable values by improving the chosen objective functions while satisfying the design constraints. Based on the optimization results, there is a significant improvement in fuel economy and emissions and the design variable values are within reasonable and expected range depending on the applied drive cycles It can be concluded that the proposed UTS PHEV powertrain can achieve the desired allelectric drive performance and improve the energy efficiency by using only one EM through the implementation of a more sophisticated EMS and ultracapacitor pack so as to reduce the negative impacts on global warming, oil depletion and the compulsory standard on fuel economy and emissions.
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