• reliability
• power factor optimization
• permanent magnets
• line-start synchronous motor
• FEM
• electromagnetic design
• direct-on-line starting-up
• cage modeling
• analytical-numerical modeling
• rotor cage
• SPM
• weak grid

This work deals with the modeling, analysis, and design of a line-start permanent magnet (LSPM) synchronous motors for fixed-speed oil-pump applications. This motor topology is proposed as valid alternative technology to the conventional three-phase induction motors and wound-field synchronous machines for fixed speed applications. The design solution is particularly attractive for applications that require high reliability and capability of operating under direct supply from a weak electric grid. A sizing procedure for surface permanent magnet (SPM) motor is presented along with the design of the embedded rotor squirrel cage to satisfy the design requirements in terms of nominal operating condition, starting capability, and dynamic behavior during the starting up. The motor performances are evaluated by means of an advanced analytical approach aiming to predict the dynamic behavior of the motor, yet targeting high accuracy and fast computation of the performance. The design and modeling approach employed is kept general in order to explore different design solutions that can be suitable for other machine sizes and applications. The electromagnetic design and mechanical considerations are proposed for a case study related to 8 MW oil-pump application. The final design is validate against a Finite Element (FE) model purposely developed. In Chapter 1 a general description of the line-start permanent magnet motor topology is introduced along with a general description of the main infrastructures needed for the oil and gas transportation and distribution. The main challenges of oil and gas stations are highlighted as well as the advantages and benefits that arose in the last decades from the intensive electrification of the sector that has enabled to reduce the operating costs, increase the reliability, and reduce the ecological footprint. In Chapter 2 the main framework of a general mid-complexity circuital modeling approach for electro-magneto-mechanical devices, suitable for long-drum electrical machines, is recalled. Particular attention is given to the representation of the rotor cage and slot openings that enables to increase the accuracy of the analytical calculations. In Chapter 3}, the preliminary sizing procedure of the motor considering its synchronous operative condition is described, which is then refined in Chapter 4 by means of a numerical implementation of the analytical model in the Matlab-Simulink simulation environment. A generic and improved sizing procedure to design PM-assisted synchronous motors with the unity-power-factor is presented.nThe accuracy of the above model is assessed in Chapter 5 by comparing the numerical results to those obtained from a 2D Finite-Element (FE) analysis, carried out using the software Simcenter MAGNET. Finally, the electromagnetic design is refined by means of FE simulations. In Chapter 6, a preliminary cage sizing is obtained through the single-phase equivalent circuit approach for induction motors and then it is further analysed numerically in the Matlab-Simulink platform to consider the dynamic response of the electro-mechanical system. A generic tool to model different cage structures is proposed, and the symmetries existing in the machine structure are exploited in order to reduce the computational burden and the model complexity. The direct line start capability is then validated with 2D dynamic FEA, considering both ideal and weak grid scenarios, overcoming the limits of the aforementioned analytical model. The design process is developed and finally assessed paying particular attention to the power quality and grid interfacing aspects.