الفهرس | Only 14 pages are availabe for public view |
Abstract In the last 60 years, the development of the rectifier and semiconductor technology has led to a variety of applications in all industries. Major applications include static power converters and drive systems. It has long been known that this equipment produces harmonics in the AC and DC power systems. The passive filter was designed to reduce the harmonics and improve the power factor. The passive filter consists of passive elements such as capacitor, inductor and resistor. However ,theses elements are limited and their values are determined and tuned or detuned to eliminate or reduce certain harmonics not all harmonics. Also the passive filters have not the adaptive ability to suppress any circuit harmonic. With advent of power electronics, a new device called active power filter is developed. The active power filter has the adaptation capability to eliminate all harmonics over wide range of operating conditions. The active power filter have two major types ,namely shunt and series active power filters. The present thesis investigates the capability of the Pulse Width modulation PWM converter system with distributed generators to operate as a shunt active power filter in order to improve the power quality and eliminate the harmonics due to nonlinear loads or distorted source or both. The harmonic equivalent circuit of sample power system is developed. The above circuit consists of harmonic current source due to nonlinear load, harmonic voltage source of distorted source, transmission line impedance and capacitor for power factor correction. The shunt active power filter is simulated in this circuit as variable admittance element. There are two control parameters of the proposed shunt active power filter, one of them is conductance while gain factor is second one. The relationship between the shunt active power filter current and harmonic source of nonlinear load in terms of shunt active power filter control variables is obtained. Also the relation between shunt active power filter current and harmonic voltage source of distorted source voltage in terms of shunt power filter control parameters is developed. A control strategy is established to estimate the two control variables of shunt active power filter. Therefore the shunt power filter currents is regulated to suppress and compensate the load harmonics and voltage source harmonics. The essential feature of the proposed control strategy is that the load voltage signal is filtered using passive filter to get the fundamental and harmonic components. Then these components are manipulated based on the two control variables of the shunt active power filter. The results are the required filter currents which are fed to the PWM converter to suppress the harmonics and regulate the dc voltage of the converter circuit. Therefore the load point voltage ( point of common coupling) and source current are filtered and will become pure sine wave. iv Moreover, the effect of the load connected to the dc side of the converter on the performance of the shunt active power filter and load voltage and source current wave forms is studied. It is found that the power quality of the power system is enhanced. To validate the effectiveness and the powerful of the proposed control strategy, the instantaneous power theory (p-q theory) is used to control PWM converter. Therefore the only harmonic currents of the converter operating as shunt active filter are injected to the power system to eliminate the load voltage and source current harmonics. A comparison between the power quality of the power system using the proposed control strategy and p-q theory is reported.In the last 60 years, the development of the rectifier and semiconductor technology has led to a variety of applications in all industries. Major applications include static power converters and drive systems. It has long been known that this equipment produces harmonics in the AC and DC power systems. The passive filter was designed to reduce the harmonics and improve the power factor. The passive filter consists of passive elements such as capacitor, inductor and resistor. However ,theses elements are limited and their values are determined and tuned or detuned to eliminate or reduce certain harmonics not all harmonics. Also the passive filters have not the adaptive ability to suppress any circuit harmonic. With advent of power electronics, a new device called active power filter is developed. The active power filter has the adaptation capability to eliminate all harmonics over wide range of operating conditions. The active power filter have two major types ,namely shunt and series active power filters. The present thesis investigates the capability of the Pulse Width modulation PWM converter system with distributed generators to operate as a shunt active power filter in order to improve the power quality and eliminate the harmonics due to nonlinear loads or distorted source or both.The harmonic equivalent circuit of sample power system is developed. The above circuit consists of harmonic current source due to nonlinear load, harmonic voltage source of distorted source, transmission line impedance and capacitor for power factor correction. The shunt active power filter is simulated in this circuit as variable admittance element. There are two control parameters of the proposed shunt active power filter, one of them is conductance while gain factor is second one. The relationship between the shunt active power filter current and harmonic source of nonlinear load in terms of shunt active power filter control variables is obtained. Also the relation between shunt active power filter current and harmonic voltage source of distorted source voltage in terms of shunt power filter control parameters is developed. A control strategy is established to estimate the two control variables of shunt active power filter. Therefore the shunt power filter currents is regulated to suppress and compensate the load harmonics and voltage source harmonics. The essential feature of the proposed control strategy is that the load voltage signal is filtered using passive filter to get the fundamental and harmonic components. Then these components are manipulated based on the two control variables of the shunt active power filter. The results are the required filter currents which are fed to the PWM converter to suppress the harmonics and regulate the dc voltage of the converter circuit. Therefore the load point voltage ( point of common coupling) and source current are filtered and will become pure sine wave.Moreover, the effect of the load connected to the dc side of the converter on the performance of the shunt active power filter and load voltage and source current wave forms is studied. It is found that the power quality of the power system is enhanced.To validate the effectiveness and the powerful of the proposed control strategy, the instantaneous power theory (p-q theory) is used to control PWM converter. Therefore the only harmonic currents of the converter operating as shunt active filter are injected to the power system to eliminate the load voltage and source current harmonics. A comparison between the power quality of the power system using the proposed control strategy and p-q theory is reported. |