Abstract
This paper studies the voltage fluctuation of dc-link generated in a 13-level cascaded neutral point clamped (NPC)/h-bridge (CNHB) with single-phase active front end (AFE) at the input side of each cell. The voltage fluctuation may deteriorate the power factor (PF) and current harmonics in the system. In this paper, new adaptive filters are proposed to overcome the problem. The center frequency of the proposed filters can be automatically varied, which allows to eliminate the specific harmonics in the dc-link well rather than the conventional one. Therefore, it can reduce the fluctuation of dc-link and maintain high PF and low current harmonic distortion without additional circuits externally or the current harmonics injection technique. As a result, capacitance for the dc-link can be optimally designed, and even cost and volume of the system can be reduced. This paper analyzes reasons of increasing voltage fluctuation theoretically and the conventional filter and proposed two types of adaptive filters are compared. In addition, the optimal design method of the dc-link capacitor necessarily used in NPC/h-bridge is presented. To verify the principle and feasibility of the proposed control method, a simulation and experiment are implemented with the CNHB system.
Highlights
In high power applications such as medium voltage motor drives, wind turbines, solar cells and vehicles etc., the multilevel topologies introduced in [1] have been widely applied to reduce the harmonic current on the grid, downsize the physical filter size and mitigate the switching losses of the used devices, in comparison with the conventional 2-level pulse width modulation (PWM)
These multilevel topologies allow the output voltage to be closer to sinusoidal wave by increasing the number of voltage levels, and reduce the harmonic distortion reported in the literature [2,3]
In order to verify principle and feasibility of the proposed control method based on adaptive filters, the simulation has beenand developed theproposed
Summary
In high power applications such as medium voltage motor drives, wind turbines, solar cells and vehicles etc., the multilevel topologies introduced in [1] have been widely applied to reduce the harmonic current on the grid, downsize the physical filter size and mitigate the switching losses of the used devices, in comparison with the conventional 2-level pulse width modulation (PWM). These multilevel topologies allow the output voltage to be closer to sinusoidal wave by increasing the number of voltage levels, and reduce the harmonic distortion reported in the literature [2,3]. Among these topologies, the cascaded neutral point clamped (NPC)/h-bridge (CNHB). Important harmonics that are caused by switching noise, voltage fluctuation, and load variation are imposed on the input current
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