Research On Three-Phase High Power Factor Rectifier For Aviation Applications

Compared with the technique of passive filter and multi-pulse rectifier, PWM rectifier achieves closed-loop control of the input current and output voltage, and leads the development trend of high performance AC/DC converter. By now, great progresses have been made in the research of PWM rectifier, and PWM rectifiers have been used widely. In this paper, the systematic study is carried out on one-cycle-controlled (OCC) VIENNA converter applied to high power applications with mid-frequency supply. The thesis mainly focuses on the design method for VIENNA converter, the method for input current harmonic reducing, system characteristics and the system control issues.Firstly, the design method for VIENNA converter based on efficiency optimization is proposed. Based on analyzing the working mechanism of insulated gate bipolar transistor (IGBT), new switching model which can present the influence of conduction current to switching transient of IGBT and reverse recovery process of freewheeling diode is built. Based on the switching model, a loss model for VIENNA converter which includes the loss model of filter inductor, freewheeling diode and rectifier bridge is proposed. The numerical calculation of power loss is done with the Simulink/Stateflow toolbox, which ensures the calculation precision. The switching model, loss model of the converter, and the loss analysis method are verified with the test circuit and experimental prototype. With the proposed loss model, efficiency of the converter with deferent switching frequency can be calculated out. Finally, with the verified loss model, design example for switching frequency choosing based on efficiency optimization is given on a 4-kW prototype. The efficiency optimization based design method makes the selection of circuit parameter of VIENNA converter more reasonable.Secondly, the method for reducing the harmonic current of OCC VIENNA converter is studied. The average input current spectrum of single-edge-modulated OCC VIENNA converter is deduced, and it is pointed out that there are odd harmonics with single-edge modulation strategy. To reduce the harmonic current, a new scheme which parallels a leading-edge-modulated converter with a trailing-edge-modulated one is proposed, and the OCC VIENNA converter with triangular-modulation is also presented. With the above two modified schemes, the odd harmonics of input current can be reduced. The theoretical analysis and the proposed schemes are all verified with experimental results.Thirdly, the design method for the control system of OCC VIENNA converter is studied. The limitations of existing system model are pointed out, and a new large signal model is derived. The new model which reflects the voltage across filter inductor is more accurate, and is suitable for the applications with high switching frequency and also the situation with low ratio of switching frequency to line frequency. Through the analysis of the newly built model, the problems of phase displacement of input current and power limitations are revealed, the necessary conditions ensuring output voltage stability are also deduced, and the methods for calculating filter inductance with the criterion of current ripple and phase displacement angle are introduced separately. The characteristic of automatic sharing of output voltage is revealed and the parameter design method for voltage controller is proposed. All theoretical analysis is verified with experimental results.The current phase leg compensation technique for OCC VIENNA converter is proposed, and with this scheme, the phase leg angle can be reduced, and the power factor is increased meanwhile using the signal legging the input current as modulation wave only and without the need of increasing switching frequency or reducing filtering inductance. To improve dynamic response of the output voltage, the feedforward control of load current is adopted, the quick compensation to output of voltage controller with the information of load current is achieved, and the fluctuation range of output voltage is limited remarkably when load changes suddenly. Finally, the experimental results are given to verify the above two schemes.For OCC VIENNA converter with inductor as filter, the THD (Total Harmonic Distortion, THD) of input current decreased and the displacement factor increased are conflicted when the switching frequency is fixed. To solve this problem, the LCL filtering scheme is proposed. The system stability with LCL filtering scheme is studied when the grid-side and converter-side inductor current are sampled separately. Based on the analysis, the current sampling scheme is chosen, and the method for LCL filter parameter designing is also proposed. The theoretical analysis is verified with simulation and experimental results. With the proposed design method, the parameters of LCL filter can be determined when resonant frequency is chosen beforehand, which ensures the system stability and improves the quality of input current. It is reasonable that the power loss of filtering circuit can be reduced as low as possible while the input current harmonics are reduced. The experimental results show that the system resonance is damped effectively with the proposed design method, and under the condition of same load and same switching frequency, LCL filtering scheme, compared to L filtering scheme, can reduce the THD of input current and the phase displacement angle meanwhile, and the total filtering inductance can also be reduced remarkably.