Research On Model Predictive Current Control Technology Of Three-level Asynchronous Motor

It is of great significance to study environment-friendly variable frequency drive technology for improving the level of equipment manufacturing and industry control.In recent years,model predictive current control(MPCC)has attracted wide attention with the advantage of solving the multi-constraint and multi-objective optimization problem.In this thesis,back-to-back double three-level converter supplied asynchronous motor system is taken as research object,and model predictive current control algorithm and its improved control algorithm are studied.Firstly,combining NPC three-level rectifier and advantage of MPCC in multiobjective control,and taking current,neutral point potential and switching frequency control as objective function,a MPCC control system of NPC three-level rectifier is designed and delay compensation is carried out.The simulation results show that NPC three-level rectifier MPCC system has better static and dynamic performance.At the same time,the impact on the system is analyzed,and adjusting range of two weighting factors is also given,which provides a reference for theoretical derivation of weighting factor.Secondly,we take NPC three-level inverter supplied asynchronous motor system as research object.Aiming at shortcomings of traditional MPCC algorithm that the design of weighting factors is extremely complex,an improved MPCC algorithm is presented.By introducing boundaries,we design total Pareto optimal set equation and total membership function,which effectively avoid complex design of weighting factors in traditional multi-objective MPCC.The simulation results show that,compared with traditional MPCC algorithm,improved MPCC algorithm can achieve low switching frequency running on the basis of satisfactory control on other objectives,and does not need to speed a lot of time on debugging multiple weighting factors,which is beneficial to practical application of MPCC in engineering.In order to overcome disadvantages of mechanical speed sensors in asynchronous motor system,such as high price and environmental sensitivity,we combine improved MPCC algorithm with model reference adaptive system(MRAS)of speed sensorless technology.A speed estimation module based on MRAS is presented to replace speed sensors.The simulation results show that the presented system can further reduce switching frequency,and has better speed tracking performance,and robustness against parameters change.It shows that the combination of MRAS and improved MPCC algorithm is feasible and effective.Finally,experiments are carried out on experimental platforms of NPC three-level rectifier and asynchronous motor system.By analyzing neutral point potential,switching frequency and delay compensation of NPC three-level rectifier MPCC system,static and dynamic performance of asynchronous motor improved MPCC system,and low-speed performance of asynchronous motor improved MPCC system based on MRAS,the effectiveness and value of presented MPCC algorithm and improved MPCC algorithm are more fully verified.