Averaged models and control of modular multilevel converters

该研究项目涉及模块化多电平转换器的控制设计，例如用于中压驱动器或高压直流输电应用。更具体地说，要解决的问题是对称的臂之间的能量，而输出电流必须满足负载的要求。这使得系统欠驱动，这意味着输入的尺寸太小，无法控制所有变量。然而，考虑系统量在较慢时间尺度上的平均行为提供了引入更多输入变量的可能性。这一步，往往是隐含的，没有推导出一个动态模型的平均系统，是由奇异摄动方法关闭现有的科学差距。作为副作用，期望示出已知实现与要开发的平均框架兼容。预计原始系统的特征属性由建模方案的正式应用保持，使得这些属性可以在控制器设计中得到照顾。此外，平均形式主义将引入更多的输入变量比所需的，这提供了可能性，以共享的控制行动，以满足额外的目标，如考虑的限制。由于建模方案将是有吸引力的其他（欠驱动）臂为基础的拓扑结构，以及，它是希望适当地概括的结果。建模和控制设计的结果将使用现有的测试台进行实验验证。

The research project deals with the control design for modular multilevel converters which are used for instance in medium-voltage drives or for high-voltage dc transmission applications. More specifically, the problem of symmetrizing the energies between the arms is to be tackled while the output currents must meet the requirements of the load. This renders the system underactuated which means that the dimension of the input is too low in order to control all variables. However, considering the averaged behavior of the system quantities on a slower timescale offers the possibility to introduce more input variables. This step, often made implicitly and without deriving a dynamic model for the averaged system, is to be backed by singular perturbation methods closing the existing scientific gap. As a side effect, it is desired to show that the known implementations are compatible with the averaging framework to be developed. It is expected that characteristic properties of the original system are maintained by a formal application of the modelling scheme such that these properties can be taken care of in the controller design. Furthermore, the averaging formalism will introduce more input variables than required which offers the possibility to share the control action among them in order to meet additional goals such as the consideration of limitations. Since the modelling scheme will be attractive for other (underactuated) arm-based topologies as well, it is desired to generalize the findings appropriately. The results of the modelling and control design will be verified experimentally using an already existing testbench.