Three-phase Four-leg Vehicle Uninterruptible Power Supply Based On Three-dimensional Space Vector Modulation

With the development of society,the requirement of energy cleanliness will be higher and higher,and the promotion and use of new energy vehicles is bound to be a major trend.There is a great demand for uninterruptible power supply(UPS)in TV station broadcast vehicles and military loading vehicles,those kinds of vehicles should have single-phase load as well as three-phase load,In order to solve the problem of unbalanced output of three-phase inverter with unbalanced load,it is necessary to study the ups.At present,the research of three-phase inverter suppression imbalance focuses on two aspects: the main circuit topology of inverter and the control strategy it uses,which will be studied in this thesis.First of all,this thesis briefly introduces the background and significance of the project,and summarizes the current three-phase inverter topology,the unbalanced mechanism of traditional three-phase inverter and three-phase four wire inverter is analyzed and compared.It is concluded that the three-phase four leg inverter has the advantages of high DC voltage utilization,small volume and relatively simple control.Secondly,after reading a lot of literature,the control strategies of three-phase four leg inverter are compared.Compared with other algorithms,the three-dimensional space vector modulation algorithm is more suitable for digital implementation.Furthermore,the three-dimensional space vector modulation algorithms in abc static coordinate system and αβγ coordinate system are compared.The former three-dimensional space vector implementation does not involve the operation of fraction and root sign,which will save more computing resources and improve the system stability time.The three-dimensional space vector modulation algorithm used in this thesis is analyzed and studied.Then,the mathematical model of three-phase four leg inverter in abc static coordinate system is established,In order to use PI control to track the AC quantity without static error,the mathematical model in abc static coordinate system is further transformed to dq0 coordinate system,furthermore,the dq axis coupling component of three-phase four leg inverter is understood and the independent dq axis component is obtained to control separately.Based on the model in dq0 coordinate system,the symmetrical component method is used to extract the positive and negative zero three sequence components of three-phase output,and the control strategy in traditional double synchronous coordinate system is compared,In this thesis,the negative sequence and zero sequence components are transformed to the positive sequence component coordinate system by coordinate transformation,and then the three sequence components are transformed to dq0 coordinate system by the transformation of synchronous rotation coordinate system.In order to solve the phase difference of coordinate system in the coordinate transformation of traditional control algorithm and further accelerate the time of system stability,a three-phase software phase-locked loop is added in the process of coordinate transformation to better track the phase of the three sequence components and reduce the phase difference in the coordinate transformation of the control strategy.Based on the above analysis and research,the parameters of the main circuit are further designed,and the PI parameters of the double loop control are determined,and then the components in dq0 coordinate system are separately controlled by double loop control.Finally,the simulation is carried out in Matlab / Simulink.The simulation results show that the output is still balanced when the load imbalance condition is very severe.