Dynamic models of a small ac induction motor
The Power Electronics Group at Aberdeen University is working towards the provision of a complete time domain model of an electrical drive for marine applications. The model has been developed using the SABER electrical simulation software package and includes a cycloconvertor which supplies an ac induction motor which in turn drives the shaft/propeller assembly. Effects such as vibration, noise and shaft oscillations due to the cycloconvertor will be studied. This thesis reports on the development and investigation of a mathematical model of the ac induction motor which can be incorporated into the existing system model to predict vibration levels at any point on the structure of the motor. The development of the mathematical model was achieved by combining a finite element (FE) representation of the motor structure with the modal parameters of the motor extracted using modal analysis techniques. The main experimental programme on the selected motor was based on a series of parallel tests on two "identical" machines. These machines were broken apart and subjected to a modal analysis at various stages. The vibration properties of a laminated structure, similar to the core of an ac motor, were also investigated. The experimental data was then used to direct the creation of the FE models. The models were created and analysed using SDRC I-DEAS integrated software. The modal analysis results were introduced into test software, where they were "curve-fitted" to extract the modal mass, modal stiffness and modal damping parameters. The FE model, created in the finite element modelling package, was then correlated with the test model and modifications implemented until the FE and test models compared well.