Hybrid-excited permanent magnet (PM) machines utilise the coordinated operation between the PM and the field excitation current. To enhance the effectiveness of the field excitation current, iron flux bridges are applied to hybridexcited switched-flux PM machines. This study proposes a new control strategy in which the d-axis current is utilised, while the field excitation current is controlled towards zero rather than negative in the flux-weakening mode. These reference currents are determined by the voltage error regulation method. The special magnetic circuit can effectively reduce the d-axis flux-linkage by either partially short-circuiting the PM flux via the iron bridge or removing the field excitation current. The proposed method exhibits advantages, such as highly enhanced torque response in the constant torque region, extended speed range, robustness against machine parameters, and higher efficiency in fluxweakening region. The feasibility of the proposed method is verified by detailed experimental results.

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 fluxweakening mode. It is verified by the experiments and can also be implemented for other hybrid-excited machines.

This is a repository copy of Uncontrolled generator fault protection of novel hybrid-excited doubly salient synchronous machines with field excitation current control.

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