Research On Control Of Three Phase VIENNA Rectifier For High Power DC Charge Point Application

At present,the progress and development of industrial technology have further applied power electronic devices.As one of the many fields where power electronic devices are applied,the charging station of electric vehicles has been affected by power electronic devices,introducing a large number of harmonic components,causing losses and also affecting power quality.According to the current development situation of the charging pile,this thesis selects the three-phase VIENNA rectifier as the front rectifier module of the DC charging pile for research.Its switching devices are few,power factor is high,and harmonic content is low,which is widely used in the industrial field.Firstly,this thesis describes the development and evolution of three-phase rectifier.By analyzing the operation mode of three-phase VIENNA rectifier topology,the switching mode of the switch in its topology is logically equivalent to a single pole three throw switch.The mathematical model of three-phase VIENNA rectifier in three-phase abc coordinate system is established.Because it contains switching function,the design of controller is relatively difficult,so it is more convenient to simplify the control system in two-phase dq coordinate system through coordinate transformation matrix,decoupling operation,transformation to two-phase coordinate system and two-phase dq coordinate system analysis.Secondly,a double closed loop PI control strategy based on full order disturbance state observer is proposed to solve the problems such as the change of inductance parameters at the grid side of the rectifier.In the two-phase dq coordinate system,the power grid voltage phase is locked by the second-order generalized integrator phase-locked loop,and the current inner loop is decoupled.Then a full order disturbance state observer is constructed to observe the system disturbance in real time and compensate the error caused by the inductance change.Set the PI parameters of the voltage and current loops according to actual engineering requirements,ensuring that the inner current loop can quickly respond to the input current,ensuring the stability and anti-interference of the output voltage of the outer voltage loop,and verify through simulation.Thirdly,this thesis proposes a neutral point balance modulation technology based on carrier phase shifting to address issues such as unbalanced midpoint potential in rectifier capacitors.The two-phase dq modulation wave compensated by the observer is transformed into a three-phase abc modulation wave through coordinate inverse transformation.A zero sequence component containing a regulating factor is injected into it,and compared with the phase shifted triangular carrier wave to obtain the corresponding switch logic information.Based on the obtained information,the conduction and shutdown of the switch tube are controlled,which can improve voltage utilization and dynamically adjust the action time of the positive and negative small voltage vectors to maintain the midpoint potential balance.Simulation verification is conducted.Fourthly,based on the above simulation analysis,the main circuit parameters are analyzed and calculated,and device selection is carried out.The system hardware related circuit design and software implementation flowchart are provided.A system experimental platform is built based on the TMS320F28335 controller.The experimental results show that the proposed control strategy can better improve the influence of the disturbance change of the three-phase VIENNA rectifier system,make the system operate at the unit power factor,reduce the harmonic content,improve the input current sinusoidal degree of the system,reduce the DC side output voltage ripple,maintain the neutral point potential balance,and have good dynamic and static characteristics.