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Research On The Switched Reluctance Motor Drive System For Electric Vehicles

Posted on:2016-04-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:H ChengFull Text:PDF
GTID:1222330479486188Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
Under the pressures of resource shortage and environment pollusion, a lot of countries in the world develop and promote the modern electric, hybrid electric and fuel cell vehicles. Motor drive system is one of the key technologies in electric vehicles(EVs). Swithced reluctance motor(SRM) is very suitable for EVs applications due to high start torque, wide speed range, high drive efficiency, excellent fault-tolerance and low cost. However, the large torque ripple, special power converter topology and fragile position sensor also limit the application of SRM in EVs. In this thesis, according the requirements of EVs motor drive system, the design indicators of SRM for EVs, novel power converter topology, control strategies of SRM for EVs and four-quadrant sensorless control are studied. The main works are summarized as follows:The design indicators of SRM are proposed according to the requirements of electric drive system and inherent characteristics of SRM. The nonlinear dynamic simulation models are built with finite element analysis(FEA), and the optimization approaches of every indicator are put forward based on the simulation models. Then the structure parameters of SRM are optimized to maximize the developed multi-objective function and the indicators have different weight factors on the basic of comprehensive requirements of EVs. At last, an optimized SRM prototype is built. The simulation and experimental results have demonstrated the correctness of the design indicators and optimization methods.Power converter is one of the most important parts in SRM drive system. This paper proposes a novel power converter topology in switched reluctance motor drive for electric vehicles, which include a front-end DC/DC boost-buck inverter and a classical half-bridge power converter. The six equivalent circuit modes in the driving state, the five equivalent circuit modes in the braking state, and the four equivalent circuit modes in the charging state are described. In the driving state, the front-end DC/DC converter works in boost mode, the dc-link voltage is reduced for the reduction of the phase current ripple when SRM works at low rotor speed, the dc-link voltage is increased for the reduction of the commutation time, enhancing the efficiency of the system and the rated output torque capacity when SRM works at high rotor speed or heavy load. In the braking state, the front-end DC/DC converter works in buck mode, the mechanical energy can be converted into electrical energy through the asymmetric power converter is fed back to charge the battery through the front-end DC/DC converter. In the charging state, the power factor correction circuit can be constituted, the buck mode of the front-end DC/DC converter is used for charging the battery, and the harmonic proportion is reduced substantially.According to the two operating modes of EVs, speed closed-loop control in driving state and braking torque closed-loop control in braking state are proposed in this paper. In driving state, three-senction control is employed to enlarge the speed range. In order to improve the smoothness in consideration of acceleration and deceleration processes, hybrid crossover control is proposed. The turn-on and turn-off angles are regulated on-line to enhance the driving efficiency. In braking state, the braking torque closed-loop control of SRM is proposed. Hysteresis current regulator with soft chopping mode is employed to reduce switching frequency and switching loss. Torque estimator is designed to estimate braking torque of SRM online and achieve braking torque signal feedback. Feed-forward plus saturation compensation torque regulator is designed to decrease the dynamic response time and improve the steady-state accuracy of braking torque. Turn-on and turn-off angles are optimized by genetic algorithm(GA) to reduce braking torque ripple and improve the braking energy feedback efficiency.The existence of positon sensor lowers the reliability of SRM drive system in EVs. Four-quadrant sensorless control of SRM with the capacity of self-starting and wide speed range is put forward. Firstly, the flux linkage characteristic curves at 7.5°, 15°, 30° and 37.5° are measured based on the symmetry of the three-phase 12/8 pole SRM. At startup and low speed, high frequency voltage pulses are injected into the idle phase. The flux linkage is measured in real time and then the rotor position zones can be determined by comparing the measured flux linkage with the flux linkage characterisitic curves of above four special rotor positons. At medium and high speed, the rotor position can be determined by detecting the intersection of the measured flux linkage with the flux linkage characteristic curves. The propsosed method only needs to know the flux linkage characteristics curves of above four special rotor positions and neither additional hardware nor memory is required. What’s more, it can achieve self-starting, four-quadrant, entire speed range, which is very suitable for EVs application.
Keywords/Search Tags:switched reluctance, electic vehicles, design indicators, power converter, control startegies, sensorless control
PDF Full Text Request
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