Research And Realization Of Control Strategy Based On Three-phase Four-leg Matrix Converter

As a kind of AC-AC "green converter",three-phase four-leg matrix converter(3LMC)has been widely concerned by scholars both at home and abroad for its high power density,four quadrant operation,no large capacity DC energy storage link,small volume and light weight,and has broad application prospects.Three-phase four-leg matrix converter(4LMC)is a direct AC-AC converter derived from the 3LMC topology.Not only does 4LMC inherit the full benefits of 3LMC,it also has the advantage of outputting unbalanced loads.Firstly,the traditional two topologies of 3LMC are introduced respectively,and the characteristics of direct space vector modulation and indirect space vector modulation are compared and analyzed.It is pointed out that the two modulation strategies can be equivalent to each other.At the same time,the simulation model is built in MATLAB/Simulink.The simulation results show that the 3LMC output can only be balanced load,but not do anything for the unbalanced load.Secondly,in view of the inherent shortcomings of the traditional 3LMC,a direct AC-AC converter called 4LMC is proposed.Based on the topological structure,the principle and implementation process of the three-dimensional space vector modulation(3DSVM)strategy are analyzed in detail,and the mathematical derivation process of 6 switching state duty cycles is given.Based on the 4LMC with three-phase balanced load,a simulation is built in the Simulink module,and the correctness of 3DSVM strategy is verified.Then,based on the 4LMC output topology with unbalanced load,the positive and negative zero sequence separation algorithm of load current is proposed.By establishing mathematical model,the output voltage expectation expression of 4LMC is deduced,and the voltage balance of three-phase unbalanced load is realized.Aiming at the problem that the common mode voltage(CMV)of 4LMC load neutral point is too high,which will produce leakage current,destroy motor bearing and accelerate the aging of motor,this paper puts forward the method of optimizing the zero vectors selection to reduce the CMV generated by the zero vectors.Based on the 4LMC with three-phase unbalanced load,a simulation is built in the Simulink module.And the correctness of the algorithm based on load current positive and negative sequence separation algorithm and CMV suppression strategy is verified.Finally,in order to verify the correctness of theoretical analysis and simulation,a set of 4LMC experimental prototype is built.The design methods of main circuit topology,bidirectional diode clamp absorption circuit,voltage and current detection and signal conditioning circuit,IGBT drive circuit are introduced in detail.A software control system using TMS320F28335 and EP4CE22E22I7N as controller is designed,and the flow chart of software design is given.The experimental results show that the control strategy proposed in this paper is correct and feasible.