Abstract
For the discussion about the neutral point potential (NPP) control of single phase three-level rectifiers, most of the methods solve the NPP problem by adjusting the zero-sequence voltage under symmetrical load conditions. However, when one phase voltage reaches to the maximum voltage, the other phase voltage goes to the minimal voltage. As a result, the NPP control ability is limited since there is no chosen zero-sequence voltage when the modulation ratio is close to 1. It can not be suitable for some strong asymmetrical load applications, in which two DC-link capacitors are used to drive different loads separately. In this paper, a dual-degrees of freedom based PWM is proposed, which can enhance the NPP control ability for single phase three level rectifiers. Introducing a new degree of freedom, the proposed method has more choices for the NPP control. It can decrease the NPP fluctuation under the strong asymmetrical load conditions, compared with the traditional PWM methods. The simulation results ratify the correctness and feasibility of the proposed PWM method finally.
Published Version
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