A new control strategy for hybrid-excited switched-flux permanent magnet machines without the requirement of machine parameters

The hybrid-excited switched-flux permanent magnet machines (HESFPMMs) have the potential for many applications, such as electric vehicles and aerospace. However, in the flux weakening region, it is usually difficult to determine the excitation current, while the extra copper loss due to field excitation may cause significant reduction in the machine performance especially efficiency. Therefore, a new control strategy for the HESFPMMs, which can operate in both flux-enhancing and flux-weakening regions, has been proposed. It utilises a novel feature of HESFPMMs in which the flux produced by the permanent magnets can be inherently shortcircuited via the iron flux-bridges. Hence, in this proposed method, the field excitation current is set to zero in order to avoid the copper loss of the field winding in the flux weakening region. Meanwhile, it utilizes the voltage difference between the command and real voltages, and does not require the machine parameters to modify the excitation current reference in flux-enhancing mode and the d-axis current reference in flux-weakening mode. In addition, in order to improve the tracking accuracy of the excitation current, the current feedback control is employed. As a result, the proposed method can provide a smooth speed transition from flux-enhancing mode to flux-weakening mode. It is verified by the experiments and can also be implemented for other hybrid-excited machines.