| With the increasing number of power electronic devices, the problems of reactive power and harmonic pollution become increasingly serious. It has become an important research topic to eliminate grid pollution in the field of power electronics applications. With the development trend of new energy electric vehicle users, the impact on power grid cannot be neglected when the charger try to connect to the distribution system. Therefore, the power quality of the front charger circuit is required strictly. In addition, the new type charger should have the capability of modulizing and thus is suitable to be parallel, which is beneficial to the future expansion, and this will reduce the cost of the applications. Therefore, the electric vehicle charger should have high power density, high reliability and high cost performance.In this thesis, the operating principles and control strategies of three-phase high power factor VIENNA rectifier are studied according to the application requirement of electric vehicle charger. After the operating principle of VIENNA rectifier is analyzed, the mathematical models and equivalent circuits are established respectively in three-phase static (abc) coordinate, two-phase static (αβ) coordinate, two-phase synchronous rotating (dq) coordinate. Meanwhile, to solve the imbalance problem of dc output neutral-point potential, the mathematical model to keep neutral-point potential balance is also established.In this thesis, the modified double feed-forward control strategy is proposed on the basis of the double-closed loop control (i.e., voltage loop is outer control loop and current loop is inner one), the proposed feed-forward control strategy contains two parts, one is that the coefficient of feed-forward duty-cycle rate can be self-adaptively adjusted with the change of the output dc voltage, and another feed-forward control loop is constructed by the variation of output dc voltage. Thus the proposed double feed-forward control strategy can dramatically improve the dynamic response speed of the output dc voltage. The transfer-functions of voltage loop and current loop are given, and the control parameters of control loops are designed. Besides the transfer-function of neutral-point potential balance is deduced, and the corresponding control parameters are calculated.A novel digital-analog mixing phase-shifted double-frequency modulation strategy is proposed in this thesis to meet the high power density requirement of electric vehicle charger. The frequency of generating driving pulses with the proposed method is twice that of the carrier signals. Therefore, it is possible that low carrier frequency can produce much higher frequency, and there are undoubtedly much more resources to calculate compared to conventional modulation method. Consequently, the advanced and complex control algorithms can be implemented in low cost digital control chip. It can be concluded that the proposed phase-shifted double-frequency modulation strategy can not only improve the power density of the converter, but also improve the cost performance of the charger.Additionally, a method based on modified LCL filter to restrain common-mode leakage current of non-isolated electric vehicle charger is proposed in this thesis. The proposed method doesn’t introduce any extra devices, but recombines the passive components. It is obvious that the proposed method here can ensure the high reliability and high power density of VIENNA rectifier without any increasing cost. On the basis of theoretical analysis, the hardware circuit and software of VIENNA rectifier are designed in this thesis. The design methods of main circuit and control circuit are given, and software flowcharts are presented. The digital signal processor (DSP) TMS320F28035 from TI Company is chosen as the control core, and a 5kw VIENNA rectifier experimental prototype is built. Simulation and experimental results verify the theoretical analysis and the feasibility of the design. |
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