| In this thesis, direct power control (DPC) of three-phase boost-type PWM rectifiers is thoroughly investigated, simulated. The works involved in this study include the analysis of PWM rectifier DPC system and the design of new control strategies of PWM rectifier DPC system, the results derived from the works could be applied to converters, active power filters (APF), communication powers, etc.Based on the topology of the power-part of PWM rectifier DPC system, the mathematical models of DPC system are established in stationary αβ coordinates. The instantaneous power of three-phase boost-type PWM rectifiers is calculated according to the instantaneous power theory, the power control model of three-phase boost-type PWM rectifier is therefore obtained.This thesis gets the disadvantages of the general type of three-phase boost-type PWM rectifier DPC system through simulation first, then the thesis gives two control strategy.In order to improve the performance of three-phase boost-type PWM rectifiers, that is the wave of output voltage, nets side power factor of nets side, total harmonic current content, active power and reactive power, this paper designs direct power control strategy based on the three level comparator switch table.In addition, in order to increase the range of device selection, reduce switch loss, need to reduce switch frequency. According to the constraint relationship among the PWM converter DPC system power hysteresis comparator hysteresis width, switching frequency and the active power, need to increase power hysteresis width. However, when increase power hysteresis width, the system performance becomes poor, in order to solve this problem, paper design control strategy with dead zones of sector borders of rectifier DPC system.Paper established model of basing on new switch table of the DPC system in the environment of Matlab/Simulink and simulation, the simulation results show that the two new control strategy feasible, and to achieve performance requirements of system. |
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