Optimized Direct Torque Control For Axial-flux Permanent Magnet Synchronous Motor With Contra-rotating Rotors Under Unbalanced Loads Condition

Due to the development of marine science,the technological capacity of the required marine equipment is also increasing.The main source of power for marine equipment is propellers,and the main source of power for propellers is induction motors.This paper studied the optimization of a direct torque control scheme for a new type of axial-flux permanent magnet synchronous motor with contra-rotating rotors which is used on propellers under unbalanced loads condition.The dissertation firstly introduced the working principle and mechanical structure of PMSM with contra-rotating rotors,and then built its mathematical model on the basis of the traditional PMSM,laying the foundation for the optimization of the next control scheme.This paper then introduced the traditional direct torque control technology of permanent magnet synchronous motor.Based on the traditional direct torque control technology,a control strategy of counter-rotating motor based on torque angle control strategy was introduced.The position of the two rotors of the rotating motor was controlled so that the relatively backward single-side rotor can be controlled by the torque angle to realize the switching control of the double rotors.Then the MATLAB simulation experiment of its control scheme was carried out to deny its feasibility when the difference of the load of two sides was too big.At the same time,it was also found that this scheme further amplified the pulsation of flux chain and torque in the traditional direct torque control.In the traditional direct torque control,there is always a problem that the switching frequency of the inverter is too low,and the addition of the torque angle control scheme further reduces the switching frequency of the averaged single-rotor rotor,further deteriorating the control performance.Due to the problem of too low switching frequency in the whole control process,the concept of fuzzy control was further introduced in this paper.The fuzzy controller replaced the hysteresis controller in traditional direct torque control.It was expected to improve the switching frequency of the inverter,thereby further improving the dynamic response rate of the system to torque and flux linkage.Then the MATLAB simulation experiment was carried out.The experimental results show that the fuzzy control has a certain degree of improvement of the stability of the system based on traditional DTC,but when the load suddenly changes,it still cannot respond well.The reason is that the selection of membership function lacks experience and the development of fuzzy rules is not perfect.Then,in order to solve the problem of too low switching frequency,this paper introduced the sliding mode control and space voltage vector control into the traditional direct torque control scheme based on the torque angle control scheme and discarded the switching table in traditional direct torque control and increased the switching frequency of the inverter by quickly switching the system into the sliding mode state.Then the MATLAB simulation experiment was carried out for the direct torque control scheme of the contrarotating motor based on the sliding mode control.The experimental results showed that the optimized control scheme was feasible under the unbalanced load.Finally,using TI's DSP chip F28335 as the control chip,an experimental platform was built.Afterwards,based on the direct torque control of the contra-rotating motor based on the sliding module and fuzzy control,CCS 6.1 software from TI was used to compile this two control programs and carried out these experiments on axial-flux permanent magnet synchronous motor with contra-rotating rotors in the lab.The experimental results verified the feasibility of this paper's optimization scheme for direct torque control.