Phase Current Reconstruction And Fault Tolerant Control For PMSM Based On Zero Voltage Sampling

Permanent magnet synchronous motor has been widely used in many industrial servo field and military aerospace field owing to its high reliability,high power density,high control accuracy.There are usually several current sensors in the motor drive system to sample the phase currents.However,in the deep water servo system and aerospace space where there are drive space and weight requirements,reducing the number of sensors used will be meaningful.Phase current reconstruction technology can use one current sensor to achieve motor vector control,but most researches are focused on the DC-link current sampling method which has complex control algorithm,current distortion and poor per-formance at low speed.A novel phase current reconstruction technique with non DC-link sampling is taken as the research object,and the problems such as implementation prin-ciple,current reconstruction dead zone,fault diagnosis technology,fault-tolerant control strategy and current reconstruction error analysis are studied.Based on the conventional phase current reconstruction method by sampling DC-link current,the basic principle and current reconstruction dead zone are analyzed.A phase current reconstruction method called zero voltage vector sampling method is proposed.This method uses the isolated hall current sensor to sample the sum current of the two branches of the inverter during the zero voltage vectors of SVPWM.Compared with the traditional method,the phase current reconstruction dead zone of zero voltage vector sam-pling method is studied,and the influencing factors are analyzed.The simulation model and experimental platform of permanent magnet synchronous motor control system based on zero voltage vector sampling method are built,and the proposed mthod are verified.The current distortion rate is small and the current sampling points are fixed,and the motor drive performance in the low modulation region and the sector boundary area is well.The mechanism of the current reconstruction errors and the error improvement meth-ods are analyzed,there are four types of current reconstruction errors,DC offset errors,sampling phase errors,PWM switching frequency error and errors caused by current sud-den change.For the DC offset errors,a compensation algorithm based on notch filter is proposed.For the sampling phase error,the first-order holder is used to improve the per-formance.For the errors caused by the change of PWM frequency,the influence of PWM frequency on the output waveform of current sensor is analyzed,a delay sampling method is proposed.For the errors caused by current sudden change,a hybrid sampling method is proposed to increase the number of phase current reconstruction times and reduce the sampling interval in a single PWM period.Through the simulation and experimental ver-ification,the above four kinds of error compensation algorithm can effectively suppress the phase current reconstruction errors.To improve the reliability,the open circuit fault diagnosis method of the inverter is studied.Two kinds of inverter open-circuit fault diagnosis methods based on zero voltage vector sampling method are proposed.The first method is normalized average current fault diagnosis method.The zero voltage vector sampling mehtod is improved and the calculation of the normalized average PARK current vector based on phase current re-construction is studied.The second method is the fuzzy average current fault diagnosis method.The fuzzy diagnosis is used to deal with the inverter fault diagnosis variable,and the fault diagnosis information is obtained.The effectiveness of the two open-circuit fault diagnosis methods is verified by simulation and experiments.The fault control strategy of the motor based on the zero voltage vector sampling method is studied.The equations of phase currents are derive by using synthetic vec-tor method.To realize the fault-tolerant control strategy,a three-phase four-switch fault tolerant control strategy based on the equivalent zero voltage vector sampling method is proposed.The realization of three-phase four-switch SVPWM and the equivalent zero voltage vector sampling method are studied.If the neutral point is lead out,a two-phase four-switch fault-tolerant control strategy is proposed.The correctness of two fault toler-ant control strategies based on phase current reconstruction technique is verified by sim-ulation and experiments.