Research On Direct Torque Control Of Induction Motor Fed By Three-level Inverter

In recent years,multilevel inverters have broader space for development in the field of high voltage and high power variable frequency speed regulation. At the same time,direct torque control has been developed rapidly because of its simple and effective control method. Therefore,taking the induction motor as the load and the traditional two level inverter DTC system as the research starting point,this paper mainly focuses on the study of the diode clamped three level inverter DTC system.Through access to information and the overall grasp of the research status of the subject, this paper will focus on the study from the following two directions:(1) Improvement of direct torque control system;(2) Neutral point potential balance of three-level inverter.As for direct torque control system, the two main research contents are carried out:First of all, the traditional stator flux observation is a simple integration of the input signal, so the method often has the problem of DC bias and initial value error. Based on the pure integrator,the stator flux observer is improved by low pass filter and the introduction of compensation link,and the method is verified by simulation.Secondly,according to the problems of unfixed switching frequency and large torque ripple in the traditional direct torque control,a new direct torque predictive control algorithm is proposed. So the relationship between torque and flux is transformed into the relation between the straight line and the circle.Then the algorithm is realized by C language programming in S-Function module.Finally, for the emergence of the phenomenon of voltage imbalance, a control method of neutral point potential balance is proposed. The voltage space vector is re divided in the non orthogonal?60 coordinate system,and the internal sector and the external sector are taken different modulation sequence. This part is also implemented in the S-Function module, and finally verified bysimulation.