Suppression Of The Power Harmonics Produced By An A.C.Excited Generator System

As an advanced power generation and adjusting speed technology of A.C motor, A.C Excited Machines(ACEM) can be applied in power generation using a variable-speed constant-frequency scheme to produce electricity, in a pumped-storage hydraulic power plants, and in high rate variable speed drive fields. The active and reactive power of ACEM can be controlled independently and stably. The power factor can be freely varied. Modern ACEM is always excited by power electronic devices, which lead to severe voltage waveform distortion. Thus, it is difficult to find the voltage reference for the harmonic analysis. Since ACEM are always operated near to the synchronous speed, the frequency of the excited voltage is very low, even to zero. Therefore, this is the power harmonic suppression study of a complicated power supply system, in which the about harmonic general theories and methods are all inapplicable.In this paper, firstly, based on the analyzing the nature of the harmonics produced by the cycloconverter excited ACEMs, a novel concept of "power harmonic" is proposed. According to the characters of the power harmonic, a kind of self-adaptive harmonic detection method based on in-phase correlation filtering is presented, which is clear and concise in thinking. By this method the Low-pass filter can be designed easily, and by using the multiresolution and self-adaptive technique the difficulties of harmonic detection with low variable fundamental frequency and no voltage reference are worked out, which contributes much to the Implementation of harmonic suppression.Secondly, according to the character of this kind of harmonic, the solutions of power filter are deeply analyzed and an optimized topology for series connected hybrid power filter is obtained. By PWM technique, midfrequency transformer and the principle of the magnetomotive force(mmf) compensation, the problem to the transfer of the low-frequency harmonic power compensatory signal in the series APF is solved, in technique.In practical studies, finally, a hybrid active power filter based on the digital signal processor(DSP) and intelligent power module(IPM) was set up, including a cycloconverter ACEM. Based on the experimental set-up, plenty of experimental studies were conducted. The experimental results demonstrate that the self-adaptive technique, the topology of series connected hybrid power filter and the corresponding significant technologies described above are feasible and practical. As a result the studies of harmonic suppression for the ACEM system are fully succeeded to complete, from the theories to the practices.