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.
Model predictive torque control (MPTC) is developing as a high-performance control system for 3φ induction motor (IM) drives due to its simple structure and fast dynamic response. This paper proposes a sensorless modified MPTC (MMPTC) strategy to control the speed of 3φ IM drives. The suggested scheme uses an improved model reference adaptive system (MRAS) to estimate the rotor speed, motor fluxes, and improvement of the prediction model of the controller. Many experimental and simulation results using DSP/TMS320F28335 controller board and Matlab software are presented to validate the proposed control method. In addition, a comparative study for the traditional sensorless MPTC and proposed MMPTC is experimentally investigated. The presented results show low speed, torque, and flux ripples of the suggested MMPTC system at low-and high-speed ranges.
In this paper, a novel hybrid Direct Torque Control (DTC) strategy based on predictive control with optimization of the Proportional-Integral (PI) controller to improve overall performances of Three-Phase Induction Machine (TPIM) drives is proposed. The presented control technique has contained merits of the DTC method such as fast dynamic response, simple structure, less dependence to machine parameters and merits of vector control method such as high accuracy. Furthermore, a hybrid DTC method with optimal voltage vectors is presented. In the proposed control system, Genetic Algorithm (GA) is employed to obtain optimal values of the PI controller parameters. Finally, simulation results under the presented control strategy showed good performances of this method in comparison with DTC and vector control techniques.
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