This paper proposes a modular approach to the power sharing control of permanent magnet synchronous bearingless machine. The selected machine topology features a winding layout with phases distributed into non-overlapping three phase groups, a solution whose twofold aim is to increase the fault tolerance and to allow for the radial force generation. The three phase sub-windings are supplied by standard three-phase inverter, leading to a modular system architecture. A throughout explanation of the methodology used to develop the control algorithm is presented considering the torque and force control in combination with the power sharing management of the machine. Special emphasis is also placed on validating the modelling hypotheses based on a finite element characterisation of the machine electro-mechanical behaviour. The proposed control strategy is also extended to cater the possibility of one or more inverters failure, thus validating the intrinsic advantage of the redundancy obtained by the modularity of the system. An extensive experimental test campaign is finally carried out on a prototyped multi-three phase permanent magnet synchronous drive. The obtained results validate the bearingless power sharing operation in healthy and faulty scenarios, both at steady state and under extreme transient condition.
This paper investigates the single-phase opencircuit fault of a bearingless multi-sector PM synchronous machine. The mathematical model of the suspension force and torque generation is developed for both healthy and faulty conditions. The model is written in a general form and it can be easily extended to any sectored PM synchronous machine. Then, a fault tolerant control strategy is proposed and verified by means of finite elements and numerical simulations. The system shows a good fault tolerant capabilities.
This paper presents a current limitation technique for a multiphase bearingless machine featuring a combined winding system. This winding structure allows each machine phase to produce both suspension force and motoring torque. Compared to more conventional systems where two separate windings are adopted for the force and torque generation, the combined winding one leads to higher compactness and simpler manufacture. The main challenges with the combined winding configuration consist of decoupling the force and torque generation and designing a proper current limitation algorithm. The former topic has been already tackled and presented in previous publications, instead the latter will be addressed in this paper. In particular, the so called smart limitation technique will allow to prioritize either the suspension force or the torque generation. In this paper the priority is given to the rotor levitation, hence the suspension force rather than the torque is essential. The technique can be extended to give priority to the torque generation in further work and can be applied to any multiphase bearingless machine with similar winding structures. Finally, simulation results and experiment validation are provided.
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