Operation Analysis Of AC Excited Generator And Its System

AC Excited Generator (ACEG) is a doubly-fed, new type generator where both stator winding and rotor winding take part in the electromechanical energy conversion. In the view of its application as a speed-adjustable generator with constant frequency output, ACEG has broad prospects of application. The work on ACEG in our country just starts.In order to meet the requirements of hydroelectric power development of our country, a study of the operational characteristics of the ACEG as well as its system is made in this dissertation.The time-domain simulation model and software of ACEG are presented by use of lumped parameters and time-dependent electromagnetic field method, including,? Hierarchical finite element technique is introduced into the analysis of time-dependent electromagnetic field. Second-order field and circuit coupled calculation formula and software are developed where the symmetrization of coefficient matrix is realized.? High efficient, flexible element upgrading technique of the hierarchical elements in software is presented. By this technique, element upgrading for any given region (interesting region or accuracy-sensitive region) can be made automatically.? A simplified treatment for the nonlinearity of the system equations is given.? A region-separation treatment for moving-media electromagnetic field problems are presented.? An improvement to the calculation formula of the airgap elements is made.? A simulation model for cycloconverter is set up, where the practical physical structure and operation are taken into account. Thus it can deal with not only practical input and output performance, but also the practical firing logic and the changing of voltages and currents of thyristors.? A numerical simulation model as well as the software of the system including cycloconverter and ACEG are developed by the method above. It can take into account not only various transient processes of the machine but also the effect of spatial harmonics of the voltage waveform of the machine. The model contains the space distribution and time variation of different physical variables. It leads to a good simulation to the origin.Simulations of various transient processes of ACEG are made and satisfactory results are obtained.Simulation of the dynamic regulating processes of ACEG shows that: with the vector control technique of stator flux linkage orientation, fast response and command-following of active power, power factor, speed, as well as other regulating variables of ACEG system can be realized. This leads to a good performance of ACEG in speed-changing frequency-constant operation.The results of the three phase sudden short circuits calculation are as follows: the maxim stator current is in the range of 6 ~ 7 per unit, and the maximum rotor current is in the range 3-4 per unit. It shows by the simulation that the effect of harmonic voltages of cycloconver on stator currents are not significant in the transients.The emf waveform of ACEG is also investigated by means of calculation and experime, Calculation method for the magnetic field of source harmonics is developed. Effect factc affecting the emf waveforms are analyzed by means of the frequency characteristics of harmon transfer impedances and the waveform, analysis. Measures to improve the waveform of ACE by damper windings are firstly discussed and suggested. By analysis, it leads to the conclusioi that? In the view of machine's efficiency and cycloconverter's capability, it is not proper fc ACEG to operate in the range of high slip.? In the reasonable operation range of ACEG, it does not beget significant overheat due t damper windings.? The effect of the harmonics of cycloconverter on the machine is decreased significantly bj damper windings. Fundamental voltages are not affected significantly.? As the airgap of ACEG is very small, effect of tooth harmonics is large, fractional slot windings are recommended.? Alternative measure to improve the voltage waveform is to adopt twelve-pulse cycloconverter as supplied power source of the rotor.To calculate parameters of ACEG, operational impedances of ACEG are derived. And corresponding numerical method and software are created in this dissertation, which includes a numerical calculation method of constraint eddy current field with some features such as, more generalization, less CPU time required, no difficulty in eddy current area due to skin effect, direct inclusion on the end effect by frequency-dependent parameters, etc.. Tests show that the method gives good accuracy. Moreover, a decoupled formula for quasi-three dimensional traveling wave field is set up for end region parameter calculation of the ACEG. Comparison shows that the method gives good accuracy and requires less calculation time.