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This paper investigates a Vienna rectifier as a charger for series-connected battery packs. Focusing on carrier-based pulsewidth modulation (CBPWM), the ripple current flowing through the neutral point (NP) results in the voltage oscillation if the loads are resistive. To reduce the ripple of average NP current with mitigated distortion under balanced and unbalanced dc-link voltages conditions, a novel CBPWM with segmented component injection scheme (SCIS) is proposed in this paper. After dc component injection, continuous intervals for optimized component injection and clamping intervals for compensation component injection are identified. Optimized components are calculated originally based on unbalanced factor to make the average NP current zero-size in one switching period. Moreover, unique compensation components generate suitable NP current to shape the sinusoidal input currents according to the circuit analysis. In consequence, the SCIS not only keeps the input current with low-harmonic distortion, but also minimizes the oscillation of dc-link voltage under balanced and unbalanced conditions. In addition, the value of the NP current during the clamping intervals is analyzed under various operating conditions. The effectiveness and the performance of the proposed SCIS are verified by simulation and experiments. [ABSTRACT FROM AUTHOR]

This paper proposes an offset voltage injection method to compensate for AC voltage ripple at the neutral-point of a Vienna rectifier. The proposed method leads to sinusoidal input currents and has a suppression effect on the AC voltage ripple at the neutral-point by injecting three offset voltages to remove both the zero current distortion and voltage unbalance (both DC voltage and AC voltage ripple) at the neutral-point. This can result in an improvement in the Total Harmonic Distortion (THD) of the input current. The offset voltage to realize the suppressing of the AC voltage ripple is defined based on a neutral-point voltage equivalence model of a Vienna rectifier. The priority of the offset voltages is considered to avoid over-modulation. In addition, incompatibility between offset voltages is analyzed to guarantee sinusoidal input currents. By considering both of these characteristics, the proposed method injects the offset voltages in order from the higher priority to the lower priority. The performance and effectiveness of the proposed method are verified with simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a generalized design framework for three-phase Vienna rectifiers to handle the neutral point voltage balance issue. On the basis of the design framework, it is convenient to construct various neutral point voltage balancing methods with the guarantee of stability. As demonstration, three representative neutral point voltage balance approaches are presented by choosing different zero-sequence voltages. A comprehensive comparison among the three approaches is given in the aspects of input current quality, capacitor voltage fluctuation, and system efficiency. The comparison results provide guidance for constructing the most appropriate approach based on the specific requirement. Finally, simulation and experimental results verify the correctness and effectiveness of the presented approaches and the related performance analysis. [ABSTRACT FROM AUTHOR]

This paper identifies extra junction capacitances and switching commutation loops introduced by line-frequency devices (i.e., non-active every other half line cycle) in three-level ac/dc converters and investigates the corresponding effects. Junction capacitances and power loops are well known as the key factors that impact converter switching loss and device stress, thus influence device selection, power stage layout, and thermal design. By examining switching transients of the commonly used T-shaped and I-shaped three-level converters, the cause and mechanism of the extra junction capacitances and power loops are presented. The impacts on switching loss, device voltage stress, and ac-side voltage/current distortion are respectively reported and analyzed. A loss calculation scheme for the three-level converter to include that extra loss is proposed. A power layout scheme to mitigate the device voltage stress is provided. Compensation and modeling of the voltage and current distortion are also proposed. Experimental results conducted on several types of three-level converter prototypes including a gallium nitride based 115 $V_{{\text{ac}}}{\text{/650}}$ Vdc/1.5-kW/450-kHz Vienna-type rectifier and a SiC mosfet based 1-kV/10-kW/280-kHz three-level active neutral-point-clamped inverter confirm the presented effects and verify the associated analysis and solutions. [ABSTRACT FROM AUTHOR]

This paper studies the inherent relationship between currents and zero-sequence components. Then a precise algorithm is proposed to calculate the injected zero-sequence component to control the DC-Link neutral-point voltage balance, which can result in a more efficient and flexible neutral point voltage balance with a desirable performance. In addition, it is shown that carriedbased PWM with the calculated zero-sequence component scheme can be equivalent to space-vector pulse-width modulation (SVPWM). Based on the proposed method, the optimal zero-sequence component of the feasible modulation indices is analyzed. In addition, the unbalanced load limitation of the DC-Link neutral-point voltage balance control is also revealed. Simulation and experimental results are shown to verify the validity and practicality of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Compared with continuous pulsewidth modulation (PWM), discontinuous PWM (DPWM) is a preferred solution in high-frequency Vienna-type rectifiers due to its inherent characteristics of less commutation number and higher efficiency. In this article, redundant clamping modes at the same subsector with opposite effects on the neutral point (NP) voltage are presented. Then, a modified DPWM (MDPWM) scheme is proposed to regulate the NP voltage by using redundant clamping modes. Thus, the NP voltage can be controlled in each switching period to lower the NP voltage fluctuation. The implementation of the proposed MDPWM is given with variable power factors analysis. Further, the switching loss comparison of conventional space vector PWM (SVPWM), hybrid DPWM (HDPWM), and proposed MDPWM is presented as well. A simulation model was built to verify the proposed NP voltage balance with different modulation indices and variable power factors. Finally, a 10-kW prototype is built to evaluate the proposed MDPWM scheme at conversion efficiency and current total harmonic distortion (THD). Experimental results and analysis show that comparing conventional SVPWM and HDPWM, the efficiency of MDPWM is the highest. The THD of DPWM is slightly higher than that of SVPWM, and it is only 2.5% at rated output power. [ABSTRACT FROM AUTHOR]

Vienna rectifier, which is a nongenerative-boost-type rectifier, is widely used in industrial applications, such as wind turbine systems. However, the Vienna rectifier will face the challenge of reducing common-mode voltage (CMV), maintaining the sinusoidal input currents, and balancing neutral-point (NP) voltage in practice. As these issues are mutually coupled, the conventional space vector modulation (SVM) and various types of enhanced schemes cannot solve these problems properly, especially under nonunity power factor operation. To overcome these limitations, a two-layer pulsewidth modulation scheme through vector selection is developed. In the first layer of the proposed strategy, the NP voltage oscillations are mitigated by adjusting the switching sequence and dwell time of large, medium, small, and zero vectors with reduced CMV as the same in large, medium, and zero vector modulation. In the second layer of the proposed strategy, the switching states are reselected, and the dwell times are real time adjusted to eliminate the distortions in input currents. Through the aforementioned two-layer control method, CMV reduction, input current distortion elimination, and NP voltage balancing in Vienna rectifier can be realized simultaneously. The correctness and effectiveness of the proposed SVM method are verified by the experiment. [ABSTRACT FROM AUTHOR]

This study presents two methods of controlling neutral-point voltage oscillation in a hybrid VIENNA rectifier, which is composed of the parallel association of a three-phase single-switch Boost rectifier with a VIENNA-type rectifier. The neutralpoint oscillation reason has been analysed with a mathematical model. Meanwhile, the two neutral-point control methods of a simplified method based on a zero-sequence component injection and a dual-carrier pulse-width modulation (PWM) method are proposed to control the voltage deviation of the split DC-link and three-time fundamental frequency neutral-point voltage fluctuation with a decrease from ±1.6 to ±1 V, respectively. Moreover, the significant oscillation in the neutral-point voltage caused by unbalanced loads or asymmetric capacitor parameters can also be effectively suppressed by using the dual-carrier PWM method. Furthermore, the performance comparison between these two methods is provided. The experimental results show that the system after being introduced the proposed two methods still exhibits a low-order input current harmonic such as second, third, and fourth harmonics as well as the input current total harmonic distortion is lower than the standard 5%. [ABSTRACT FROM AUTHOR]