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Unbalanced ac voltages drastically deteriorate the performance of five-level flying capacitor (FC) rectifiers. Without introducing an extra buffering circuit to absorb the second-order oscillating power, it is an incompatible contradiction for realizing both negative-sequence current reduction and second-order voltage ripple suppression. In this article, based on the idea of using FCs in the rectifier to absorb the oscillating power, a second-order voltage ripple suppression strategy for unbalanced ac voltage conditions is proposed. Reducing the negative-sequence currents and suppressing the dc voltage ripples can be simultaneously realized. Simulations and experimental results verified the effectiveness and performance of the proposed scheme well. [ABSTRACT FROM AUTHOR]

Five-level flying capacitor (5L-FC) rectifier is advantageous in unidirectional power applications due to its less power devices, higher power density, better reliability, etc. To further improve the efficiency, discontinuous PWM (DPWM) methods are preferred. This article investigates a carrier-based implementation of DPWM for the 5L-FC rectifier to reduce the switching losses. Since there is always a pair of redundant switching modes that have opposite effects on the neutral point (NP) in each region of the space-vector diagram, the NP voltage regulation can be easily realized by selecting suitable clamping modes in each control period, even with unbalanced dc loads. The generated PWM sequences based on the phase disposition PWM are also optimally redistributed to realize minimal switching loss with FC voltage balancing in two consecutive carrier periods. In addition, the permissible range of unbalanced dc loads is theoretically deduced. Finally, simulations and experiments are conducted to verify the performance of the proposed carrier-based DPWM scheme. [ABSTRACT FROM AUTHOR]

Unbalanced dc-link voltages occur when five-level flying capacitor (5L-FC) rectifier has dual dc loads of different rated voltages. Compared with traditional continuous pulsewidth modulation (CPWM) strategies, discontinuous PWM (DPWM) methods have more advantages in high-frequency and high-power applications for less commutation and higher efficiency. Therefore, this article proposes a carrier-based DPWM method for 5L-FC rectifiers with unbalanced dc-link voltages. The proposed method is first analyzed in the revised space vector diagram considering unbalanced dc voltages to divide subsectors and find available clamping modes, then it is implemented by applying carrier-based PWM with injecting clamping compensation component, which greatly reduces the implementation complexity. There is a pair of redundant clamping modes with opposite effects on the neutral-point (NP) in each subsector. Thus, the NP voltage can be actively controlled by selecting suitable clamping mode in each subsector. In addition, the allowable ranges of unbalanced voltage degree and unbalanced power degree are investigated in detail. Simulations and experiments verified the effectiveness and performance of the proposed method. [ABSTRACT FROM AUTHOR]

Neutral-point (NP) voltage oscillating is an inherent problem for multilevel converters with split dc-link capacitors. In this article, a compensation component injection method based on a hybrid modulation for minimizing the NP voltage oscillations in a five-level flying capacitor rectifier is proposed. In specific, the equivalent modulation waves are first obtained by adopting an existing simplified space-vector modulation method. And a hybrid modulation which gives both the same optimal harmonic performance as phase-disposition pulse width modulation (PWM) and the same superiority of flying capacitor voltage regulation as phase-shifted PWM is adopted. Meanwhile, the solved optimal compensation component in each subsector is injected to make the average NP current equal to zero for minimizing the NP voltage oscillations. Simulations and experiments were conducted to verify the performance of the proposed compensation method based on the hybrid modulation. [ABSTRACT FROM AUTHOR]

In this article, the mechanism of current distortions for a five-level flying capacitor rectifier under unbalanced dc-link voltages is analyzed in detail. A multizero-sequence component injection algorithm based on phase-shifted pulsewidth modulation is proposed. In specific, the proposed modulation algorithm divides the fundamental period into clamping and continuous intervals. Considering the inherent topological constraint that the terminal voltage is related to the polarity of the phase current, clamping compensation component is added to three-phase reference signals for clamping one-phase reference signal to zero in order to mitigate current distortions near the zero-crossing points during the clamping interval. Each flying capacitor voltage is regulated by adjusting two switching modulation waves with independent compensation component injection to avoid affecting the average terminal voltage. To improve the quality of dual dc voltages, optimized compensation component is simultaneously injected to three-phase modulation waves for minimizing the ripple component of the average neutral-point current during the continuous interval. In addition, the allowable ranges of both unbalanced voltage degree and unbalanced power degree are theoretically deduced. Finally, simulations and experiments are conducted to verify the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) has drawn more and more attention and has many applications, such as wireless electric vehicle charging systems, which require high power, high efficiency, and high power factor. In this paper, a single-stage WPT resonant converter with bridgeless boost power-factor-correction (PFC) rectifier is proposed to improve efficiency and power quality of line input, and reduce production cost and complexity for high-power WPT system. The bridgeless single-stage topology is creatively proposed to apply in WPT system, which is much more advantageous than conventional two-stage WPT converter with individual boost PFC stage. [ABSTRACT FROM PUBLISHER]