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This study proposes several easy-to-implement control strategies when seven-phase axial flux brushless DC machines with trapezoidal back electromotive forces operate in normal and faulty modes by taking into account constraints on voltage and current. The constraints are related to the converter and machine design in terms of maximum values of current and voltage. The considered faults are cases in which one or two phases of the machine are open-circuited. Numerical computations based on analytical formulations are applied to obtain torque-speed characteristics, including the flux-weakening operation. The methods determine current references to ensure the torque optimisations while currents and voltages are within their limits. The usefulness of the methods is verified by numerical results. [ABSTRACT FROM AUTHOR]

This paper presents an extension of previous methods in order to find electrical series connections between multiphase machines, allowing the independent control of each one of them. These new electrical series connections explore the symmetrical disposition of the phases of even-multiphase machines, allowing the inversed connection of some of the phases, different from the direct connections as it was previously done. Therefore, electrical series connections of two symmetrical six-phase or of four symmetrical ten-phase machines are now possible. Besides that, this new solution ensures a natural independent control of permanent-magnet synchronous machines even if the back electromotive forces (back EMFs) generated by the rotor are not sinusoidal, without need of special machine conception or supplementary control strategy. This control independency is mathematically proved using the decomposition of multiphase machines in fictitious diphase and homopolar machines. Experimental results are presented to show the functioning and the advantages of this new coupling for two symmetrical six-phase permanent-magnet synchronous machines (PMSMs). [ABSTRACT FROM AUTHOR]