حبیب رستمی

One of the basic conditions in distribution systems is the voltage regulation within the allowable range which is very important for proper functioning of electrical equipments. In Addition constant changes and getting higher or lower in voltage level over permitted range will have a devastating effect on electrical devices. Industry, in search for modernization, has integrated electronic devices , programmable logic controllers , process control equipments and robotics as their main operational equipments. Since development of these sensitive technologies, voltage sag has been known as a major problem in power quality and rise of voltage has been known as a minor problem. So in this thesis, several aspects of voltage sag and rise, such as different reduction techniques to reduce the effects of them, have been studied. Recent researches tend to investigate D-STATCOM technique to decrease the voltage drop and fluctuations in a power distribution system. The controllers based on flexible electronic devices like Distribution Static Compensator have proved that are quite effective in reduction of voltage drop and fluctuation, regardless of the size of the system. Temporary electromagnetic models have been introduced in order to investigate quality of power. A new control scheme based on PWM has been implemented to control electronic gates in dihedral voltage source converter (VSC) which are used in D-STATCOM.In this thesis, pulse width modulation is imporved by injection of third-order harmonics and also hysteresis controller is used instead of PI controller which is simulated in PSCAD. This PWM control scheme needs only to measurments of voltage and this feature makes it suitable for power usages in distribution voltage level. This control scheme has been tested in a wide range of operating conditions and observed that in every case, it is very strong and robust. D-STATCOM is a device that promises a great future in the power system to reduce the power quality problems