Graphical Diagram for Subspace and Sequence Identification of Time Harmonics in Symmetrical Multiphase Machines

The use of multiphase motor drives is an increasingly important strategy nowadays. These multiphase machines are usually modeled by a reference frame transformation to avoid the cross-coupling of variables. This transformation decomposes the original n-dimensional vector space into orthogonal subspaces. Mapping the voltage and current harmonics into the subspaces in distributed machines is important because it allows to identify which components are related to the torque and which ones just increase the machine losses. The sequence identification of each harmonic is also important in closed-loop current harmonic compensation to set the controllers. In addition, the harmonic mapping is interesting in multimotor systems to know how harmonics from one machine can affect the other machines in the system. In this paper, a simple graphical method for time harmonic subspace and sequence identification is proposed. This method is valid for symmetrical machines of any phase number n, it provides full subspace and sequence identification and it can be used in multimotor systems. Experimental results using a five- and a six-phase motor in single-drive configuration and a series-connected two-motor six-phase drive validate the proposed method.