Inverter-fed induction machine dynamics.

The study includes the analysis and investigation of inverter-fed squirrel cage induction machine drives. The particular drive used was a 120° square wave inverter feeding a Tubular Axle Induction Motor developed for rail traction by British Railways. The system and its operating modes, including self-excited braking, are described. The conditions under which self-excited braking can be achieved are investigated both theoretically and experimentally and upper and lower limits to the range of permissible rotor speeds are found by several analytical methods. An original analogue model of the inverter is developed which is suitable for the investigation of inverter firing algorithms. A simpler and more efficient model is developed for the investigation of commonly used inverters. A two axis model of the induction machine is described and used to produce an analogue simulation. State-variable analysis is used to predict the steady-state waveforms and the transfer functions of the system. A simple method of predicting the frequency response of a linear or linearised system is described. Steady-state sinusoidal analysis is used to predict the limits to self-excitation. Results from the various methods of analysis are compared with each other and with results from the real system in both the transient and steady-state modes of operation. The results from the analogue model are found to give best agreement with those from the real system in both modes. Inverter losses are found to affect the boundaries of self-excitation. The possibility of using the analogue model in the development of micro-processor control for the traction system is discussed