Study On The Key Technology Of Power Conversion For High-speed Low-voltage Starter/Generator

The technology of high-speed starter/generator can reduce the volume and weight of system,enhance the power density and reliability of system,can also promote the development of energy efficient industries and distributed generation technologies.The two-stage high-speed low-voltage starter/generator power conversion is studied,including the intermediate frequency PWM rectifier technology,wide input voltage range of bi-directional DC-DC converter,small-capacity DC bus capacitors rectifier technology and interaction of converter cascaded and so on.An overview of the research status of the starter/generator system and the high-speed motor is presented.The latest developments of intermediate frequency PWM rectification technology and bi-directional DC-DC converter are introduced.The practical application problems of the small-capacity DC bus capacitors rectification,input current ripple of bi-directional DC-DC converter and DC bus voltage stability in motor runing are demonstrated.The predictive direct power control strategy of three-phase voltage source intermediate frequency PWM rectifier is proposed.Firstly,the output characteristic of high-speed low-voltage motor is analyzed.The high frequency mathematical model described by switching function and low frequency mathematical models of the three-phase voltage source PWM rectifier are introduced.According to the instantaneous power theory,the power model of three-phase voltage source PWM rectifier is derived.According to the design specifications of system,circuit parameters are calculated.In order to reduce the influence of harmonic stage power converter for high-speed motor,a predictive direct power control strategy three-phase voltage source intermediate frequency PWM rectifier is proposed based on internal model principleAn input voltage feed-forward control strategy for the wide input voltage range bidirectional Four-Switch Buck-Boost(FSBB)converter is studied.The amplitude and frequency of output voltage from high-speed low-voltage generator is wide,the FSBB converter is used to regulate DC voltage after the rectifier bridge.Based on switching average model,the low frequency small signal models of the non-ideal FSBB converter under synchronous switching control model are built under different operation modes and the main transfer function of the control system is also derived.The influences of the input parameters on the control system are analyzed.The duty cycle under the control strategy is changed by the input voltage disturbances directly.The influence of input and output parameters and right half plane(RHP)zero on the stability of control system is described,the best design approach of system parameters under voltage control mode is given.An input voltage feed-forward(IVFF)method is proposed to reduce the disturbance on the output voltage caused by input voltage.The load power feed forward control strategy of small-capacity DC link capacitor in three-phase voltage source intermediate frequency PWM rectifier has been studied.Based on instantaneous power theory,both the active and reactive power flow PWM rectification system are analyzed.The relationship between filter capacitance and equivalent resistance line,bus voltage magnitude and load power is studied in the dq coordinate system.For the instability problem of small-capacity DC bus capacitance system,based on the load power feed forward the predictive direct power control strategy is proposed to achieve reliable operation of the small capacitance system.The input current frequency ripple suppression method of front stage DC-DC converter is studied when the motor operate in constant speed.The propagation mechanism of secondary ripple current in FSBB converter under voltage control and current voltage double closed loop control are analyzed.In order to avoid the ripple current transmit to the front stage,based on the impedance matching principle of passive filter,a passive LC filter tuned is added in the middle DC bus link which can provide zero impedance branches.Based on the output current back gain Ai(s)= iin(s)/io(s),an average current control method with a notch filter in the outer loop is proposed,which is an active control strategy and can effectively suppress the low-frequency input current ripple.An optimal motors control strategy which can enhance the DC bus voltage stability of cascaded system is presented.First,the high-speed low-voltage motor maximum torque current ratio control mathematical model is built,and then the DC input impedance two-stage starter/generator converter is derived.Based on impedance matching criterion,the stability of the two-stage converter system is analyzed.In order to improve system stability margin,the fluctuation of bus voltage is used to compensate the control voltage in dq components of the motor,which can improve the stability of the DC bus without additional hardware while there is no change of the control structure.A lot of simulation and experimental have been done,of which the results show the correctness of theoretical analysis and effectiveness of the control method designed.Contents of this thesis provide certain basis for the design and optimization of high-speed motor starter/generator system.