(A) flux and speed control with parameter estimation for an indirect field oriented induction machine drives

Abstract

The induction machine drive system can be characterized as a multi-input multi-output system, which is complicated by the fact that it is highly coupled and ninlinear. Because the system is nonlinear, the system poles are changed by the operating point so that it is difficult to ensure that the system is stable over the entire operating range by using the scalar control methods. Also, the dynamic performance of the induction machine can not be easily improved by using the relation of control variables, for example, the profile between voltage or current and frequency. The foregoing limitation can be overcome by applying a field oriented control method. In the field oriented control system, the current components controlling the rotor flux and torque are decoupled so that the indepengent rotor flux and torque controls are possible as in a separately excited DC machine. Therefore, the current controller has direct influence on the drive performance and its design requires particular considerations. The basic requirements are the fast dynamic response during the transient state, the optimal switching pattern and lower current ripple in the steady state, and the stable performance under the variations of load parameters and operating conditions. To satisfy the above mentioned requirements, several current controllers with the input voltage feedback are proposed in chapter III. In this dissertation, the indirect field oriented control method in which the rotor flux is estimated from the stator voltage, current, and excitation frequency is used. This method is based on the slip frequency control, where a slip calculator is used to establish the rotor flux angle with respect to the stator MMF. If the rotor time constant used in setting the slip frequency is incorrect, the machine performance from the veewpoint of flux and loss is degraded. Thers are two detuning dffects. One is a seady state operation with the incorrect values of flux and slip. Another is a transient ...