Sobhan Mohamadian

Load-commutated inverters (LCIs) are reliable and efficient drives to supply synchronous motors in high power industrial applications. However, inadequate attention is dedicated to this type of drive especially for higher phase numbers and in the case of faults. It is a proven fact that the fault tolerance of the voltage-source inverter (VSI)-fed multiphase machines is enhanced as the number of phases increases. However, the same principle is not necessarily applicable to the LCI-fed multiphase synchronous machine drives. As it will be shown in this paper, a thyristor failure may cause the drive instability and the situation can be more critical for higher phase numbers. In this paper, open-circuit faults and their consequences are investigated and compared for symmetrical and asymmetrical multiphase LCI-fed drives. Also, a new control strategy is proposed to restore the drive stability in the case of open-circuit faults in LCI-fed drives. Simulation results for a five-phase drive show that the control system can efficiently keep the machine synchronism in the event of phase open-circuit faults. © 2018 IEEE.

Hardware-in-the-Loop (HIL) simulation is a technique that is being used increasingly in the development and test of complex systems. Real-world testing of an intricate system in a field like power plant can be challenging, time-consuming, expensive, and hazardous. HIL emulators allow engineers to test devices, thoroughly and efficiently, in a virtual environment with high reliability and minimum risk of defect. In this paper, the complete electric power system (including generator, turbine-governor, excitation system, transmission lines, transformer, external grid and related loads) is implemented in MATLAB/Simulink environment. Different virtual instrument (VI) pages are modeled in the graphical programming language of LabVIEW which enable fast and reliable measurement functions, such as data acquisition, archiving, real-time graphical display and processing. Interaction between MATLAB and LabVIEW is accomplished by generating a Phar Lap ETS Targets *.dll file which enables two software to exchange real-time data. Also, a real 1518 kW excitation system is considered as a test case for introduced HIL system. This equipment is connected to LabVIEW software through a National Instrument PXI technology. Different scenarios (electrical frequency/active power change, voltage step response and etc.) are simulated in the designed Power System Emulator (PSE). Validity of the implemented model for excitation system is verified by finding good matching between MATLAB and HIL simulation results. IEEE

Nowadays, in addition to providing active power to the local loads, photovoltaic systems are helping the grid to control the point of common coupling voltage. In this paper, a new version of instantaneous reactive power theory has been proposed to control the point of common coupling voltage. The advantages of using this method are the absence of phase-locked loop and the application of simple calculations to raise the speed of the system response. Moreover, the proposed method is in such a way so that it allows the system to mitigate the symmetrical and asymmetrical voltage sag and swell; consequently, the quality of power delivered by photovoltaic system to the grid will be improved. On the other hand, the proposed structure, in addition to increasing the reliability of power injection, maintains providing of balanced active power in the presence of unbalanced reactive power without the need to additional controllers. To validate the proposed structure, the system has been tested on IEEE 33-bus radial distribution grid and the results are presented from a dynamic simulation by using MATLAB/SIMULINK. According to the results, the proposed method regulates the point of common coupling voltage with a response time of about 0.2 second that is faster than conventional control strategies. Copyright © 2017 John Wiley & Sons, Ltd.

Load-commutated inverters (LCIs) with woundfield synchronous motors (WFSMs) form one of the most applicable drive topologies, and in some cases the only one, in high-power medium-voltage applications. In this paper, a novel method is introduced to determine the switching instants of the thyristors which is done through the stator flux estimation. Compared to other frequent switching schemes, the proposed method is simple, less parameter sensitive and free from some additional circuits or transducers. Also, a comprehensive flux observer is presented to estimate the stator fluxes. Some disadvantages concerning the other flux observers such as initial conditions and dc drift problem, large time constant at high speeds and phase and magnitude error in low speeds are eliminated by the proposed observer. Simulation results show the validity of the proposed switching scheme and flux observer in a wide speed range. © 2017