Multi-agent voltage balancing in modular motor drives with series-connected power electronic converters

Modular motor drives can be considered as multi-agent systems, in which the agents can work together to reach a common goal. One agent in such a modular motor drive consists of only a subset of the machine phases and power electronic converter modules, and is equipped with a dedicated controller. When the dc-links of the different agents are connected in series to a single voltage source, giving rise to a so-called stacked polyphase bridges converter, the power electronic converter components can have low voltage ratings. However, a voltage balancing controller must ensure that the total dc-link voltage is distributed evenly among the agents when working in motoring mode. The goal of this research is to propose a multi-agent voltage balancing algorithm based on dynamic average consensus, which depends solely on local computations, local measurements, and neighbour-to-neighbour communication. The scalability and reliability of the modular hardware are hence extended towards the control. Simulations and experimental results on a 4 kW modular axial-flux PMSM demonstrate the feasibility of the concept.