Abstract
Traditionally, only the output power quality specification is emphasized. Not much attention was paid to the harmonic pollution and power factor at the input AC line. However, with the increasingly rigid power quality requirement, more and more researches are devoted to the harmonic reduction and power factor correction in recent decade. As far as high voltage AC/DC converters are concerned, a multi-level hysteresis current controller is indeed a nice strategy to solve the about problem. However, existing multi-level hysteresis current controllers were designed based on an intuitive idea to choose a proper one among many voltage levels for the controllers. As a result, the resulting current errors may be outside the error bounds for some time period. In view of these, a novel multi-level hysteresis current control strategy is proposed based on the current error derivatives to improve the drawback of the existing methods. In this thesis, first, a neutral-point-clamped (NPC) AC/DC converter configuration is chosen and some related control strategies proposed recently are roughly reviewed as starting background. The corresponding theoretical defect is also pointed out and demonstrated by simulation. Then, a novel multi-level hysteresis current control strategy is proposed with sound theoretical basis to correct the above drawbacks. In order to keep the merit of easy implementation of hysteresis current controllers, an approximate three-level hystersis current controller implementation is also proposed to avoid calculating the complex current error derivatives. Finally, a prototype is constructed and some experimental results are presented for verifying the feasibility of the proposed controller.