Research On Fault Diagnosis And Common Mode Voltage Suppression Method For Five-Phase Drive System

With the advancement of science and technology and the development of society,the important role of electric motors in national production and life has become increasingly prominent.The rapid development of modern power electronics technology has broken the limitation of the traditional three-phase power supply system,which has attracted extensive attention to the multi-phase motor drive system.Compared with the traditional three-phase motor drive system,the multi-phase motor drive system has many advantages such as large power output,high reliability,flexible control,and small torque ripple.Therefore,it is widely used in ship propulsion,aerospace,electric vehicles,locomotive traction and other key fields.The fault of the multi-phase motor drive system not only affects the reliable operation of the system,but also may cause serious economic and even personnel losses.In addition,the common mode voltage problem brought by the PWM inverter in the multi-phase motor drive system not only affects the safe and stable operation of the power grid,but also seriously affects the life of the motor winding insulation and bearing.Based on the National Natural Science Foundation of China(51707007),this paper takes the five-phase motor drive system as the research object.The single-phase open-circuit fault diagnosis and the common-mode voltage suppression method of the five-phase induction motor drive system are deeply studied theoretically and experimentally.Firstly,the mathematical model of five-phase induction motor in natural coordinate system is established.The simulation model of fault diagnosis of five-phase induction motor is built by Matlab.According to the characteristics of the third harmonic plane current trajectories during the single-phase open-circuit fault of five-phase drive system,the fault factor used by fault detection is designed,the position angle of the current trajectory for fault identification is defined,and the thresholds of the corresponding variables are set and detected.A single-phase open-circuit fault diagnosis method for five-phase motor drive system based on the detection of harmonic current plane is proposed,which realizes the single-phase open-circuit fault diagnosis of the five-phase motor drive system.The simulation results prove the correctness of the theoretical analysis of the proposed method.Then,the PWM principle of the five-phase two-level voltage source inverter and the generation mechanism of its common mode voltage are analyzed in detail.Based on the comparison analysis of two existing P WM strategies,the idea of suppressing the common mode voltage is obtained,that is the PWM strategy is used to minimize the sum of the switching states.Furtherly,a SCPWM strategy based on the mirrored sawtooth carriers that can effectively reduce the common mode voltage amplitude and frequency is proposed.In addition,the effects of dead zone and harmonic injection are analyzed detailedly.The conclusion that the dead zone does not produce common mode voltage spikes is obtained.Moreover,the feasible region of third harmonic injection is drawn.A five-phase drive system simulation model based on five-phase two-level voltage source inverter was built by Matlab/Simulink.The simulation results are consistent with the theoretical analysis.Finally,the proposed fault diagnosis method and SCPWM strategy are verified on the five-phase induction motor drive experimental platform.The experimental results show that the single-phase open-circuit fault diagnosis method of the five-phase motor drive system proposed in this paper can complete the fault diagnosis within 18%of the current fundamental period,and keep no mistake during the transient conditions of the commanded speed and load torque,which reflects the rapidity and robustness of the method.Meanwhile,compared with the traditional SPWM strategy,the SCPWM strategy proposed in this paper can effectively reduce the common mode voltage amplitude and frequency by 80%and 40%,respectively.On the other hand,for the SCPWM strategy,the harmonic suppression technique can be used to optimize the THD of phase currents,and injecting the third harmonic in the feasible region does not affect the suppressive effects of the common mode voltage.