New operation modes of modular multilevel converters with output voltage modulation significantly reducing the module capacitor requirements - II

在即将到期的项目期内，验证了一种准2电平（Q2L） PWM工作模式，用于控制支路电流的模块化多电平变换器（MMC）。它使模组电容器大幅减少到其通常尺寸的几个百分点。这在成本、体积和重量方面都是一个决定性的优势。同时保留了MMC的许多优点，如可扩展性、冗余、在模块中使用低成本的低压半导体等。特别是，输出电压的步骤和相关的dv/dt也仅限于单个模块的值，这对于绝缘设计和轴承电流风险的长电机电缆的电力驱动器非常重要。与MMC相比，Q2L-MMC的一个重要缺点是输出电压和电流的失真增加，类似于传统两点逆变器的情况。这就是建议的后续项目开始的地方。该概念应扩展到具有低电平的准n电平MMC，从而显著降低输出波形失真。在目前的项目中，控制支路电流的方法已经可以转换为准三电平（Q3L） MMC，并在仿真中得到了验证。此外，还模拟了一种较省力的Q3L- mmc混合拓扑结构，以及Q3L向模块化矩阵多电平转换器（MMMC）的转换。基于此，拟开展的后续项目目标如下：在与现有解决方案进行评估和比较之前，需要对提到的变体进行实验验证。此外，该概念应扩展和推广到n电平转换器，包括在实验室中验证Q5L操作。在混合变体的情况下，除了已经提到的拓扑概念外，另一种尚未详细研究的方法很有吸引力。这种新方法提供了许多潜在的优势，甚至优于传统的多电平转换器。作为拟议项目的一部分，这一创新概念也将被研究和评估。

In the expiring project period, a quasi-2-level (Q2L) PWM Operating mode for Modular Multilevel Converters (MMC) with controlled branch currents was validated. It enables a drastic reduction of the module capacitors to a few percent of their usual size. This is a decisive advantage for cost, volume and weight. At the same time, many advantages of MMC are retained, such as scalability, redundancy, use of low-cost low-voltage semiconductors in the modules, etc. In particular, the steps in the output voltage and the associated dv/dt are also limited to the values of a single module, which is important in electric drives with long motor cables for insulation design and the risk of bearing currents. An important disadvantage of the Q2L-MMC is the increased distortion of the output voltages and currents compared to MMC, similar to the conditions in conventional two-point inverters. This is where the proposed follow-up project starts. The concept shall be extended to quasi-n-level MMC with a low number of active levels, thus significantly reducing the output waveform distortion. In the current project, the approach with controlled branch currents could already be transferred to a quasi-3-level (Q3L) MMC which was validated in simulations. In addition, a hybrid Q3L-MMC topology with less effort, as well as the transfer of Q3L to a modular matrix multilevel converter (MMMC) have been simulated. Based on this, the aim of the proposed follow-up project is as follows. The variants mentioned need to be validated experimentally before an evaluation and comparison with existing solutions takes place. Also, the concept shall be extended and generalized to n-level converters, including validation of a Q5L operation in the laboratory. In the case of hybrid variants, in addition to the topology concepts already mentioned, another approach is attractive that has not yet been studied in detail. This new approach offers many potential advantages, even over conventional multilevel converters. As part of the proposed project, this innovative concept will also be researched and evaluated.