Research On Fault-Tolerant Operation And Speed Sensorless Control Strategy Of Multi-Phase Induction Machine

Multi-phase machines are gaining increasing popularity because of their distinct advantages over three-phase alternatives,such as high power at low voltage,high reliability and improved control dimensions.This paper takes asymmetric six-phase induction machine as an example to study its fault-tolerant control strategy and speed sensorless technology.The winding structure and harmonic characteristics of multi-phase motor are analyzed.Taking asymmetric six-phase induction motor as the research object,the mathematical model of the motor in natural coordinate system is deduced.Through space vector decoupling transformation,the mathematical model under harmonic basis is established.According to different connection modes of the middle line,the space decoupling transformation matrix of the motor after single-phase open circuit is deduced.On the basis of this,a unified breaking fault mathematical model of multi-phase induction motor is established,and the torque ripple after phase absence is analyzed.In order to realize fault-tolerant operation of multi-phase induction motors,the fault-tolerant control strategy of multi-phase induction motors is studied from three aspects: The first one is based on the idea of optimal current control.According to the principle that the total magnetic potential of the stator remains unchanged,the magnitude and phase of the residual effective phase current are calculated according to different optimization objectives.At the same time,in order to avoid the shortcomings of hysteresis control,proportional resonance control is adopted in the current loop to realize the zero-static-error tracking control in the phase coordinate system.The second one deduces the mathematic model in dq coordinate system based on the theory of field-oriented control according to the mathematic model of αβ subplane after open-phase.According to the rotor flux orientation,the stator current excitation component and the torque component are decoupled,and the field-oriented control of multi-phase induction motor after phase-absence is realized by the modified rotation transformation.The third is based on the principle of direct torque control,which analyses the change of voltage vector after single-phase open circuit,and chooses the large voltage vector at the outermost layer to realize the dynamic control of torque and stator flux.In order to avoid the problem of excessive torque ripple and unstable switching frequency,calculate flux variation to get reference voltage vector,the driving signal pulse is obtained by carrier modulation strategy.A observer based SMO is established in the αβ plane of the multi-phase induction machine,the process of flux linkage and speed identification is deduced,and the robustness of the observer to parameter and load disturbances is analyzed.The system chattering is reduced by using saturation function instead of symbolic function.By modifying the sliding mode observer under fault state,it can satisfy the open-phase operation of the multi-phase induction motor and improve the robustness and reliability of the system.The hardware experiment platform of multi-phase induction machine control system is built,and the correctness and validity of the fault-tolerant control strategy and speed sensorless control technology proposed in this paper are verified by simulation and experiment.