Research On Design And Control Method Of PMASynRM For New Energy Vehicles

The development of new energy vehicles is to alleviate the worldwide energy consumption and environmental pollution problems.The motor drive system is one of the key technologies in the new energy vehicle(EV),the permanent magnet assisted synchronous reluctance motor(PMASyn RM)is suitable for the drive of EV because of its characteristics such as rare-earth-free,wide speed range,high driving efficiency and strong fault-tolerant ability.However,large torque ripple,lower torque density,power density,and lack of control methods limit the application of PMASyn RM in EV.According to the demand characteristies of EV motor drive system,this paper studies on the index of PMASyn RM design,comprehensive performance optimization method,high efficiency control method under rated speed,field-weakening control and faulttolerant operation.The main contents of the paper are as follows:This paper presents a driving cycle testing method of EV,which provides a reference for the design of driving motor for EV.This paper analyzes the demand characteristics of EV motor drive system,compares the difference between EV and fuel vehicle’s power system,and deduces the relationship between EV power system and motor operating parameters.Secondly,this paper analyzes the current mainstream of several kinds of fuel vehicle driving cycle test methods and speed distribution,compares the characteristics between each method.This paper presents a method for calculating the drving cycle curve of EV with probability distribution equilibrium.The proposed method takes the New European Driving Cycle(NEDC)test curve as reference,studies the probability distribution of the energy point in the whole test of the fuel vehicle,and converts it to the EV,deduces the efficiency point distribution of the driving system characteristic of the EV,and puts forward the test method of operating condition of the EV.The market-oriented EV supports the feasibility of the proposed test method.Based on the Taguchi orthogonal test method,the structural design of the rotor asymmetrical motor is proposed with the main objective of torque ripple weakening.Firstly,the influence of the structure characteristics of double layer magnetic barrier on the performance of the motor is analyzed by finite element analysis(FEA).This paper presents 15 design factors for PMASyn RM with double layer magnetic barrier rotor structure,and extracts 3 design levels for each factor through the influence of various design factors on the performance of the motor.The L54(21×315)orthogonal test table is designed based on Taguchi method,which solves the problem that many factors(315)are difficult to solve out comprehensive test.The torque ripple and efficiency of the motor are weighted,and the initial optimization structure of the motor is obtained.The initial structure is optimized locally two times,the stiffness of the structure is improved and the mass ratio of the adjacent poles is balanced,which improves the stability of the rotor structure at high speed.The simulation and experimental results verify the optimization of the designed motor in the aspects of torque ripple and efficiency distribution.Aiming at the new mathematical model of PMASyn RM and the structure characteristics of the motor,an efficient control method based on torque prediction at base speed is proposed.Based on vector control,the realization process and control effect of PMASyn RM maximum torque per ampere(MTPA)control are studied.A MTPA control method based on torque predictive control(TPC)is proposed for the characteristics of the motor,which selects the optimal switching signal by predicting the future state and the corresponding output effect,and improves the dynamic performance of the voltage vector selection by DTC control.By setting the MTPA value function constraint,the dq-axis current in the steady state of the motor is constrained to the MTPA trajectory,which obviously improves the system efficiency.Based on the structure of the motor,the global loss model of the motor is established,and the optimal efficiency control method based on TPC is proposed,which is the further improvement of the system efficiency than the TPC-MTPA control.Simulations and experiments have verified the fast response and steady-state efficiency of the TPC-MTPA and TPCMEPA control methods of the PMASyn RM below the rated speed.This paper puts forward the field-weakening(FW)and the fault-tolerant control method of PMASyn RM,which satisfies the actual demand of the new energy vehicle operating condition.According to the mathematical model of PMASyn RM,the basic theory of field-weakening control and the constraint relation of voltage and current are deduced,and the PMASyn RM weak magnetic expansion speed method based on voltage outer loop for dq-axis current coupling compensation under vector control is studied,which realizes the field-weakening control without dependence on motor parameters.The TPC-MTPA method under the base speed is extended to the fieldweaking region,and the TPC-MTPA-FW control method is proposed.The value function of TPC is reconstructed in the field-weaking region,and the full speed region of PMASyn RM under TPC control is realized through the switching of value function,and the proposed method has higher dynamic response speed and convergent precision than vector control in full speed domain.Analyse of the characteristic change after PMASyn RM demagnetization,the TPC-MTPA-FW constraint condition is reconstructed in full speed region,and the fault-tolerant control based on EKF rotor flux observation is realized.Simulations and experiments verify the effectiveness of the full speed region control and the robustness of the algorithm after demagnetization.PMASyn RM is very suitable for electric vehicle applications with its stable structure,low cost,designed excellent control methods.