Modeling and power quality improvement of turbo-expander driving an induction generator

Today, the energy crisis has caused to recover the energy which is normally wasted in gas pressure reducing process in gas stations of cities or power plants. This work is done by turbo-expanders in parallel with gas regulating valves. In electrical industry, these devices drive generators to produce electrical power from the main process. In this paper a model for turbo-expanders is presented. This model is more efficient and simpler than the older model which surmounts the need for making complicated lookup tables. Because of instantaneous varying of domestic consumptions, environment temperature and other effective parameters, turbo-expander inlet gas pressure and mass flow-rate vary with time and consequently extracted power has time variant specification and causes some power quality issues such as voltage flicker, voltage sag, etc. So, this system is simulated and power quality issues are investigated for a fault occurring in point of common coupling (PCC). Then, the flicker in electrical waveforms due to change in input pressure or mass flow rate is investigated and finally a D-STATCOM is designed and added at PCC to improve the power quality problems of the system.