The Research On Design Of Urban Rail Vehicle Auxiliary Inverter System

The auxiliary inverter system is an important part of electrical equipment in the urban rail vehicles,which is responsible for providing electric power to all the auxiliary equipment loads,so its importance is self-evident.The ?/Y0 frequency transformer is often selected in the existing auxiliary inverter system construction to achieve the purpose of isolation and providing neutral line.But one of the frequency transformer's prominent shortcomings,which is its large size and great weight,makes the entire auxiliary inverter system's size and weight even larger.In view of this problem,the paper designs a set of relatively lightweight system which uses high-frequency isolation transformer,and it can significantly reduce system's size and weight.This paper firstly summarizes the main circuit topology of the existing auxiliary inverter system.The designed lightweight system construction is finally selected after comparison and analysis,including the phase-shifted full-bridge converter with a high-frequency transformer and the three-phase four-leg inverter.And the system's parameters are calculated according to the technological requirements of the auxiliary inverter system.In the following part of this paper,the small-signal model of the high-frequency isolated phase-shifted full-bridge converter is established,and the related transfer function is then deducted.Thus the converter's closed-loop control system is designed.For the four-leg inverter,its three-phase voltage is unbalanced with unbalanced loads,as a result of that the negative and zero sequence components both superimpose on positive sequence voltage.To solve this problem,the paper designs an improved sub-sequence decoupling control strategy which is based on the symmetrical components method and the double-rotation coordinates transformation.This strategy can respectively suppress both the negative sequence and zero sequence voltage components,leaving only the positive sequence component to achieve the purpose of three-phase load voltage's balance.After analyzing the four-leg inverter's 3D-SVPWM algorithm,the paper proposes a simplified algorithm which can reduce the amount of calculation by half.Finally,the DC/DC conversion system's model and four-leg inverter system's model are respectively established in the Matlab/Simulink.The former model verifies that the DC/DC conversion system using phase-shift control can reach the purpose of isolation and regulation.At the same time,it can realize zero-voltage switching,reducing the switching losses.The latter model verifies that the four-leg inverter system can output three-phase balanced voltage no matter the load is balanced,imbalanced or mutational.And the three-phase output voltage can meet the requirements.In conclusion,this auxiliary inverter system contains a high-frequency isolation phase-shifted full-bridge converter and a four-leg inverter.It achieves a lightweight system construction and provides the high-quality three-phase four-wire voltage,solving the problem of three-phase voltage imbalance due to complex auxiliary electrical loads.This paper provides favorable conditions for this scheme's practical application by further simplifying the complex control system.