| With the development of new energy technologies and great success of hybrid electric vehicles,the application of hybrid powertrain in rail transit has become a popular point.This thesis is relying on National Technical and Scientific Support Projects for the "12th Five-year Plan" ?"Research and Development for key technologies and prototype of Hybrid Electric Multiple Units(HEMU)".Based on the electrical stability and energy stability of the hybrid system,following parts were studied:bi-directional DC/DC converter modeling,stability analysis and optimization of bi-directional DC/DC-inverter cascade system,hybrid system characteristics and energy management strategy.The research results were verified by model simulation and prototype test.First,the bi-directional Buck/Boost circuit is selected as the topological of the bi-directional DC/DC converter.According to the switching element average method,the Buck and Boost converters for small signal model are built,then transfer functions and open loop impendance are defined.Besides,a double close-loop control system of inner-current outer-voltage is set up and based on closed-loop small-signal control diagram,the closed-loop input/output impedance expression is derived for following study.The impedance ratio criterion of the stability analysis of the cascade system-MiddleBrook criterion and forbidden zone theory are introduced.Based on the impedance Bode curve and the impedance ratio Nyquist curve,the bi-directional DC/DC cascade system stability is analyzed in full speed range.The influence of the negative impedance characteristic of the inverter load on the stability is analyzed qualitatively.Based on the closed-loop front-class input and after-class output impedance of the system,the influence of circuit parameters and control parameters such as inductance and capacitance on the stability of DC-side is emphatically studied,simulated and verified.Based on those all above,the improvement measures of the stability of the virtual capacitor are put forward.Then,the energy demand of the system is obtained by traction calculation.The hybrid power capacity configuration and the key components are selected.The characteristic of diesel generator and the power battery are studied as the energy management reference and basis.The uniform expression of drop voltage for the diesel generator and fuel consumption curve under different state are established,and SOC partition diagram is planned.Considering the operating characteristics of HEMU and the principle of low fuel consumption,this paper proposes a logic-based threshold management strategy,and focuses on the study of subsystem control methods,completing diesel generator speed control,battery charge and discharge control based on sag characteristics and load power control.The validity of the control strategy is verified by the simulation model,and the energy distribution and coordination between the power supply and the load are realized.Finally,the energy management results are discussed in different working conditions.It is proved that the hybrid energy management and control strategy can realize the reasonable flow and distribution of energy to meet the train operation demand. |
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