Study On Control Strategy Of VIENNA Rectifier In Three-phase Unbalanced Voltage Grid

In recent years,VIENNA rectifier due to its advantages of easy voltage boost,less switching devices and high conversion efficiency,widely used in high-power pre-stage rectifier such as wind farm,electric vehicle charging piles and aircraft electrical power supply.During the three-phase VIENNA rectifier operation,grid due to some faults may lead to three-phase grid voltage unbalance,affects the equipment proper functioning.Therefore,it is necessary to study the control strategy of VIENNA rectifier under the three-phase unbalance.In order to ensure VIENNA rectifier to operate reliably in unbalanced grid,this thesis mainly studies VIENNA rectifier’s working principle,modulation,mathematical model,control objectives and control methods in the unbalanced power grid,and completes the following work:Firstly,analyze VIENNA rectifier’s basic working principle and switching state,introduce the simplified three-level SVPWM modulation strategy,and derive AC and DC side mathematical model.Secondly,introduced three-phase unbalanced theory.According to the mathematical model of VIENNA rectifier in dq coordinate and αβ coordinates,introduce the current inner loop control strategy based on voltage oriented control in sliding mode,and respectively according to inhibit negative sequence current,active double frequency component and reactive double frequency component of the three control targets,get current instructions,establish VIENNA rectifier sliding mode in grid unbalance voltage oriented control strategy.Introduce direct power control in the αβ coordinate based on predictive control strategy and get control voltage output model according to control objective of inhibit active power double frequency component,establish VIENNA rectifier three-phase unbalance control strategy based on direct power predictive control.The results show that this algorithm can effectively improve the current waveform and reduce the total distortion rate of current harmonics in different control targets under the three-phase grid voltage unbalance.Finally,set VIENNA rectifier main power circuit parameters,design and select power devices and build VIENNA rectifier hardware experimental platform.Through design software program to verifies the feasibility of the control strategy.