Research On Control Strategy Of Active Neutral-Point Clamped Three-level Rectifier With Low Frequency

Multi-level topology are widely used in high-voltage power occasions because of its low harmonic content,energy flowing in both directions and other advantages.In the high-power system,loss of power device is large and it’s essential to reduce the switching frequency.However the reduction of switching frequency would cause an adverse impact on the dynamic performance of the system.This paper takes ANPC(Active Neutral Point Clamped)three-level rectifier as the research object,SPWM modulation is studied,and focuses on studying mathematical model,current regulator design with low switching frequency.Firstly,mathematical model of control system and loss distribution of ANPC three-level rectifiers are analyzed in this paper.Different communication of three-level ANPC and NPC rectifiers are analysised,three-level rectifiers have more communication mode in the zero state.And the zero switching states are selected ti solve the loss unbalance problem of NPC rectifiers.This paper analysis three SPWM modulation strategies of ANPC three-level inverter.Secondly,the influence of low switching frequency on the control system is analyzed,and complex vector mathematical model is established.At low switching frequencies,the decoupling are intensified of conventional PI current regulator and the PI current regulator with feedforward decoupling.Through the transfer function,system coupling term can be canceled by complex vector controller completely.Good dynamic and static characteristics is proved by bode diagram and unit step response when the switching frequency is reduced.Thirdly,model predictive control is studied for good dynamic and steady state performance with low switching frequency.According to the better current follow ability and the midpoint potential balance control,the optimal voltage vector is obtained by rolling the 27 kinds of voltage vectors.Zero switching state can be achieved by loss of rolling optimization.The control method is improved for making the loss,control performance and switching frequency achieve the optimal state.In addition,based on the model predictive control,the fundamental wave and the harmonic quantity are extracted by the sliding fourier transform.The effectiveness of the control algorithm is verified by simulation.Finally,by building an ANPC three-level rectifier platform.Three SPWM modulation strategies,complex current control and model predictive control are took place.The results verify the feasibility and effectiveness of the ANPC three-level inverter control strategies which are analyzed in this paper.