Study Of Nonlinear Problem And Operating Energy Savings For Induction Machine

Electrical machine is a complex system of conversion between electricity and mechanical energy characterized by nonlinear-in-parameter, powerful coupling .multi-variant and period. The nonlinear problem of machine has been long investigated ,which may be one of critical keys to improve machine operating quality. At present induction machine consume over 60 percentage of total electricity in the world,and the energy-efficient motor technologies have been paid more attention to from the viewpoint of energy crisis and environment. As far as our country is concerned which is short of natural resources and make use of energy at a low efficiency level , it has a great significance to increase the operating efficiency of motor for the economic and social reasons.This dissertation explores the nonlinear problem and maximum efficiency of induction machine. Firstly, the effect of hysteresis and saturation upon ac machine is discussed, and hysteresis delay angle by which magnetic density delay magnetic force at the zero point because of hysteresis is detected and can be measured by no-load experiments, a close evaluation of hystresis iron loss is presented by an significant expression as well. Secondly, a novel method of linearizing nonlinear problem is proposed by introduction of differential coefficient of nonlinear flux to linear flux .Motor state equations including hysteresis and saturation are carefully derived, and more accurate mathematical model of induction machine is created which can be used as a basis of analysis. Simulation and experimental results are compared to validate this novel model. And then, the research of PWM voltage source motor drive system is carried out . Owing to symmetry, state analysis is easy to be handled by the help of matrix conversion between 6 voltage space-vetor sectors.and a model for motor powered by voltage PWM source is set up ,which is taken account of hysteresis and saturation as well as dead zone. Lastly, a DSP-based experimental variable-frequency power system is built up, and on-line calculation of voltage space vector PWM in real time is developed and can be expressed in unique equations by means of matrix conversion of 6 space sector into one sector. Further more, the operating efficiency mechanism of motor is investigated in detail . A significant expression is obtained with consideration of iron loss, it is shown that maximum efficiency can be achieved by reasonable allocation of active and reactive power in drive system. Experimental results are given to validate the theoretical results. Other optimum approaches are also discussed. Finally , according to the idea that maximum efficiency can be obtained by reasonable allocation of active and reactive power ,based on field-oriented techniques a strategy aiming at maximum efficiency for induction machine is put forward, which result in high quality of operation and fast response of torque. Simulation model, including PWM inverter ,machine incorporating hysteresis and saturation and field-oriented controller having straightforward goal of energy saving and adjustable speed , is created ,the simulation results show that this strategy not only have good performance ,but also realize the goal of optimum efficiency.