Research On High-performance Power Converters And Vibration Suppression For Switched Reluctance Motors

The requirements of the motor system performance and reliability become increasingly higher due to modern industry developments.Compared to traditional electric machines,switched reluctance motor(SRM)is a very competitive motor,which has a simple and rugged structure without any rotor windings and permanent magnets.Moreover,owing to further inherent advantages including high efficiency,high reliability,excellent fault-tolerance ability,and high starting torque in initial accelerations,SRMs are considered to have a wide prospect in industrial applications.Therefore,this paper focuses on developing high-performance and high-reliable SRM drive systems.Converter design,current sampling and control,fault-tolerance control and vibration reduction have been investigated in details.For power converter topology,a new integrated multilevel converter of SRM is proposed for plug-in hybrid electric vehicle applications.The proposed converter combines the power sources in the SRM driving system with only two IGBTs and two diodes based on the asymmetrical half-bridge converter,without extra capacitors and inductors.Multilevel operation modes and diverse working modes are achieved and the battery can be flexibly charged in motoring,braking and standstill conditions.The motor torque and efficiency are both improved due to the multilevel voltage.The proposed converter is convenient to manufacture and replace because of its modularized structure.It is more compact and the power density is also improved.This new converter topology is also suitable for other multiphase SRM systems.For phase current sampling,a novel phase current reconstruction method based on dc-link current sampling for SRMs is proposed in this paper.The phase currents can be reconstructed by using only one current sensor to sample the dc-link current.In this method,a small change is made to the circuit connection of the conventional asymmetrical half-bridge converter.In the two-phase excitation region,two kinds of high frequency pulses with phase-shift and large duty-cycles are injected into each down switch,respectively,and two analog to digital(A/D)converters are triggered in the injected PWM pause middles for phase current reconstruction.The phase currents can be reconstructed by the sampled dc-link current and the turn-on and turn-off information,which can be directly used for current chopping control.The synchronization between the injected PWM frequency and current sampling frequency ensures high-quality reconstructed phase currents.Because of the extremely short turn-off time of the injected PWM,it would not cause the phase current distortion.Compared to the traditional motor systems,the current sensors are greatly reduced by employing the proposed scheme,which also provides a high-reliable fault-tolerance method for SRM systems.Based on the proposed phase current reconstruction scheme,some further advanced technologies are presented,including online sensorless position estimation for SRMs using one current sensor,low-cost direct torque control for SRMs with dc-link current sampling,and fault diagnosis for SRM drives with a single current sensor.In order to enhance the motor system reliability,a novel and flexible SRM fault-tolerance topology based on a relay network is proposed for fault-tolerance control under multi-type converter faults.A single-phase inverter is connected to the conventional asymmetrical half-bridge converter by the relay network according to the faulty conditions,which provides rapid fault diagnosis,high-performance fault tolerance and advanced control functions.The fault-tolerance topology can rapidly bypass the faulty circuit and make full use of the healthy parts of the converter,to reduce the torque ripple under fault-tolerance operation and maintain the balanced operation of the SRM system.The developed topology can also support the extremely faulty conditions,which is suitable for wide applications.In order to reduced the SRM vibration,the radial force distributed on the stator yoke under different skewing angles is extensively studied.Four different SRMs including conventional SRM,skewed stator SRM,skewed rotor SRM and skewed stator and rotor SRM are all designed and fabricated.The motor vibration,efficiency and torque for the four SRMs under high-and low-speed operations are compared in details.It is suggested that skewing the stator is more effective to mitigate the vibration than skewing the rotor in SRMs.Finally,the simulation model and experimental setups are built up.These simulation and experimental results are presented to confirm the validity and effectiveness of the proposed schemes.