Research On Modular Cascade Machines System For Electrical Vehicles

Modular cascade machine(MCM) system is a novel electric driving system, in which each machine unit works like a battery. Each machine is independent. Several motors work together as a system. Different external characteristic can be fitted by module number or parameters changing. A series of machine units can be designed with standard modular structure and port, thus, variant demands of power can be fitted by module number change instead of machine redesign. In this way, different load property could be satisfied, false tolerance property and reliability are enhanced as well as selecting, using and maintaining is simplified.When applied in electric vehicles(EV), MCM system can match the characteristics demand, which has EV friendly performances of torque-speed and high efficiency area of electric driving system. This paper researches MCM system EV application, including sizing method of the system, design method of machine unit and torque distribution strategy for system efficiency improving.Sizing methods for MCM system are studied to obtain the specification of each motor fitting electric driving system performance demands which achieve a reasonable machine configuration. Firstly, an electric driv ing system simulation model is created, so the external characteristics of the MCM system are determined. Secondly, the sizing methods of single-mode based on efficiency fast estimation method and multi-mode based on genetic algorithm are investigated separately. Take high efficiency area and system weight as objective functions to get the parameters of multi-machine. Solutions of machine sizing for different EV types are given. In order to realize efficiently sizing, an efficient estimation method is put forward, which laid a theoretical foundation for machine unit design and application.For characteristics of MCM system and requirements of electric driv ing system, the topology for MCM system reliability improving and machine unit design method for power density increasing and efficiency area expanding are studie d. Two kinds of MCM system topology are proposed. Design features are analyzed to give design requirements respectively. In a view of efficiency, different types of motors in MCM system are compared. Research demonstrates that combination of low-speed permanent magnet machine and high-speed induction machine is more suitable for MCM system. An optimization design method of machine unit based on genetic algorithm is proposed and machine units with high efficiency and high power density using fractional-slot concentrated winding are designed. On the basis of the design method, multi-mode MCM system with two machines is designed for control strategy research. At last, the FEA simulation results verify the accuracy of the efficiency fast estimation method.Running at high efficiency area as much as possible of the machine unit is the foundation of MCM system efficiency improving. However, frequently switching to machine unit will lead to torque ripple and low reliability, even additional loss. Torque distribution strategies of MCM system are studied. Vehicle simulation model of dynamic control is established. The basic idea of the control strategy is determined. Different operating modes are analyzed. Research on the torque distribution strategy based on optimal efficiency is taken as reference and evaluation of other control strategies. In order to improve the real-time performance of the system, the torque distribution strategy based on rule-based is put forward, which reduces the amount of computation and improves the operation condition of machine unit. On the basis of these researches, a torque distribution method based on fuzzy control strategy is proposed, which can make machines unit torque distribution reasonable for being more economical and dynamic. Resea rches show that MCM system energy consumption is lower than single motor driving system. Thus, EV with MCM system is more economical if dynamic performance permit s.Prototype of MCM system is designed and produced for sizing and design methods verification. External characteristics and machine unit efficiency Maps are tested. Comparisons on experimental results, FEA simulation and efficiency fast estimation method show that the proposed design method and efficiency estimation method are feasible and accurate. The MCM system real-time control experiment platform based on Matlab/Simulink and d SPACE hardware in the loop is built and the control strategy experiments are finished. The experiment results show that the proposed fuzzy control strategy is suitable for MCM system, which can raise system running efficiency and avoid machine unit frequent switching to improve machine unit operating condition. All above are consistent with the theoretical analysis.All above researches show that MCM system can be optimized not only according to EV actual power requirement but also by adjusting the number of modular motors to fit the different power demands to reduce the research and development time and cost. With this optimized control strategy, low speed-high torque and high speed-high power can be realized easily by sizing different machine unit. What’s more, each machine unit is independent, so when one motor false happens it is easy to cut or replace false unit, which improve vehicle reliability, false tolerance and reduces maintaining cost. With these advantages, MCM system has a good application prospect in EVs, wind power generation, ship propulsion and other fields of large speed range, complex drive condition or high reliability requirement.