Modeling and Power Quality Improvement of Grid Connected Induction Generators Driven by Turbo-Expanders

Nowadays, the energy crisis has forced the need to recover the energy which is normally wasted in industrial processes. Gas pressure reducing process in city or power plant gas stations is one of these processes in which the energy is wasted. 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-expander is presented. This model which utilizes an online calculation method is more efficient and simpler than the older offline model which surmounts the need for making complicated lookup tables prior to calculation. 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 the 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 at the point of common coupling (PCC). Then, the flicker in electrical waveforms due to change in input pressure or mass flow rate is investigated. Since the power quality problems due to disturbances are considerable, a D-STATCOM is designed and connected at PCC and it is shown that the STATCOM has improved the power quality problems of the system.