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Fault‐tolerant drives have been gaining increasing attention due to the need to enhance the reliability and robustness of electric drive systems, particularly for safety critical applications. However, in postfault control, it is often necessary to derate the machine, that is to reduce the torque and/or flux currents, to satisfy the current constraints of the power electronic devices. For induction motors, there are different approaches to quantify the current components in postfault operation while maintaining a stable operation within the current constraints. The efficiency enhancement of a faulted drive through flux current reduction is one of the methods reported in literature, however, the details of power components, that is, achievable torque and speed, are not addressed. This study broadly investigates the effect of flux and/or torque current partitioning on postfault capability of polyphase (three and more phases) induction machines in terms of achievable torque and speed. It is demonstrated that the magnetising inductance characteristics, which depend on the machine design and its power rating, have a profound effect on the choice of postfault current partitioning, and hence the machine performance. Theoretical discussion is supported with experimental verification using three‐phase and symmetrical six‐phase induction motors. [ABSTRACT FROM AUTHOR]

This study proposes a new architecture of flywheel energy storage system (FESS) which can be implemented at generating unit (GU) level (e.g. wind turbine) or scaled up for application in grid‐side converter (GSC) stations of a multi‐terminal direct current (MTDC) system. The proposed architecture suppresses DC voltage leaps under grid faults, and performs power levelling duty at grid connection points. When implemented at GU level, the proposed FESS features a doubly‐fed induction machine (DFIM) – the flywheel machine – where its six stator winding terminals are connected in series between the grid and the GSC. The flywheel converter is of partial power rating, and is connected to the DFIM rotor. When employed at an MTDC GSC station, several submodules are connected to build an FESS station. The study proposes the control concept and the general topology of the FESS station. The performance parameters of the system are tested under normal and abnormal operating conditions. Results and analyses indicate smooth dynamic operation, the economic advantage and the improved fault ride‐through capability because of the proposed system. [ABSTRACT FROM AUTHOR]