Improved Model Predictive Torque Control Of NPC Three-Level Inverter Fed Permanent Magnet Synchronous Motor System

NPC three-level inverter fed permanent magnet synchronous motor system has the advantages of high output voltage quality,low switching loss at the same switching frequency,high power density and simple structure,so it is widely used in high-voltage and high-power driving occasions.Model predictive torque control can achieve multi-objective and multi-variable optimal control,which is easy to handle system constraints.However,the tuning process of weighting factors of each variable of this control method under NPC three-level inverters is complex,and the control performance will decrease when the imbalance of neutral point voltage is large.This paper studies and do some researches for the two problems.In this paper,the deadbeat equations are first deduced,and the torque term and the flux term in the cost function are unified into the stator voltage term,which eliminates the dimension of torque and flux linkage.Then,the cost function is equivalent to the distance difference between the reference stator voltage vector and other basic voltage vectors.For the neutral point voltage term,the partition control of neutral point voltage imbalance is used in this paper.When neutral point voltage imbalance is small,only the optimization of flux linkage and torque performance is considered.When neutral point voltage imbalamce is large,it is preferentially suppressed.The phase and amplitude change of medium and small vector needs to be considered.According to the imbalance of neutral point voltage,the equations of new basic voltage vectors are derived.Then,the amplitude and phase angle of small and medium vectors are recalculated in each control period,which are used to divide sectors dynamically.At the same time,according to the different control priorities in each neutral point voltage imbalance zone,the influence of every large,medium and small vectors on the flux linkage,electromagnetic torque and neutral point voltage can be analyzed and used to optimize the finite control set and reduce the alternative voltages,which simplifies the algorithm to some extent with eliminating the weighting factor of neutral point voltage.In this paper,the simulation and experiment platform of three-level NPC inverter-fed permanent magnet synchronous motor is built,and the relevant algorithms are validated.Both simulation and experimental results show that the improved control method proposed in this paper can effectively reduce the fluctuation of torque,flux and current when neutral point voltage is large with eliminating weighting factors.Also,the proposed method can surpress the imbalance of neutral point voltage fast with improving the control performance of this system.