This study presents a concept of modulation of a single-phase seven-level neutral point clamped (NPC) converter with natural DC-link voltage balance and symmetrical DC-link capacitors discharge. The method is analysed in a single-phase full-bridge inverter composed of four-level diode-clamped legs (4L-FBCLD) which utilises three capacitors in a DC-link. Under the classic pulse width modulation (PWM) technique, the discharge of DC-link capacitors is unequal in a converter operating with active power. The proposed modulation assures symmetrical discharge of the DC-link capacitors and is achieved in a two-stage design. In the first stage, the carrier-based phase disposition PWM technique with modified carriers is used. In the second stage, the pulses are directed to suitable switches with the use of a state-machine decoder. The switching patterns are different in each level of modulation and are used to trigger natural balancing in the converter on the first and third level of modulation. This study presents the concepts of switching patterns, PWM generation, as well as the simulation and results of the experiment. The latter demonstrates the operation and feasibility of the 4L-FBCLD, symmetrical DC-link capacitor discharge and natural balancing in the converter.

中文翻译：

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具有四电平脚的单相NPC逆变器中的自然直流链路电压平衡和新颖的调制方法

这项研究提出了一种具有自然直流母线电压平衡和对称直流母线电容器放电的单相七电平中性点钳位（NPC）转换器的调制概念。该方法在单相全桥逆变器中进行了分析，该逆变器由四级二极管钳位管脚（4L-FBCLD）组成，该管脚在DC链路中使用了三个电容器。在经典的脉冲宽度调制（PWM）技术下，在以有功功率运行的转换器中，直流母线电容器的放电是不相等的。所提出的调制方式确保了直流母线电容器的对称放电，并通过两阶段设计实现。在第一阶段，使用具有修改后载波的基于载波的相位配置PWM技术。在第二阶段，使用状态机解码器将脉冲定向到合适的开关。开关模式在每个调制级别上都不同，并用于在第一和第三调制级别上触发转换器中的自然平衡。这项研究提出了开关模式，PWM产生的概念，以及仿真和实验结果。后者演示了4L-FBCLD的操作和可行性，对称的直流母线电容器放电以及转换器中的自然平衡。