Power system harmonic instability and countermeasures

In recent years some local power systems went to unstable, performed as voltage and frequency swing, extended to trip, local system outage. This paper confirms that some of them caused by harmonic instability phenomenon, the reason is high power electronic equipment produce large amount of harmonics, and then system voltage heavily distorted result in phase locking failure of some power electronic equipment. The basic principle of a robust phase locking method of power electronic equipment must treat fundamental frequency waveform and positive components of the reference voltage only. For the sample voltage with unbalance and harmonics, this paper uses slide Fourier and slide symmetrical component method, these methods can get the fundamental positive component voltage with minimal computing procedure. According to the need of series connected devices, this paper introduces the current extraction methods and the effective harmonic detection methods.