| Summary: | The thesis presents solutions to improve the performance of a partially levitating bearingless permanent magnet synchronous machine with a multi-three-phase winding. A combined winding topology, which consists of three independent three-phase sub-windings, is installed in the stator where each phase contributes to both the suspension force and the motoring torque. This work focuses on control algorithms, including fault-tolerant controls, a current limitation technique, and a current-sharing technique.
Firstly, the thesis presents an analytical formulation of the force and torque generation in healthy operative conditions. Following, the three-phase and single-phase open-circuit fault conditions are also analysed. The analytical model of the machine is presented in a generic matrix form so that it can be applied to any machine with a multi-three-phase winding structure if the coupling among sectors is negligible. The fault-tolerant control algorithms address the issues of open-circuit faults of an entire three-phase sub-winding, of a single-phase in a three-phase sub-winding, or of two phases belonging to two different three-phase sub-windings. The theoretical analysis is verified with both Finite Elements Analysis and experimental tests.
Then, the thesis proposes a current limitation technique. The main challenges with the combined winding configuration consist of decoupling the suspension force and torque generation and designing a proper current limitation technique. The latter is required in order to maintain the machine in safe operative conditions according to its current-voltage rating and its operative thermal limits. This thesis addresses the limitation technique based on the analytical models, considering both healthy and faulty conditions. In particular, the proposed current limitation technique allows prioritising the suspension force, which is considered a safety-critical output with respect to the torque in order to avoid the rotor touchdown. Numerical simulation results and experimental validation are provided to validate the algorithm.
Finally, the thesis proposes a modular approach for a current-sharing control of the machine. A thorough explanation of the methodology used is presented, as well as control algorithms to consider the torque and force control combined with the current-sharing management of the machine. Particular 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 to the possibility of one or more inverters failure, thus validating the intrinsic advantage of the redundancy obtained by the system's modularity. An extensive experimental test is finally carried out on a prototyped machine. The obtained results validate the current-sharing operation in either healthy or faulty scenarios, both at steady-state and under transient conditions. These outcomes show the potential of the proposed strategy to increase the versatility of fault-tolerant drives applied to this machine topology.
|
|---|