الفهرس 
Ch1 IntroductionOnly 14 pages are availabe for public view
 |  | from | 107 |  |  |
| | | from | 107 | | |
Abstract
The tendency of connecting the Power Electronic loads and distributed power plants through Power Electronic converters is increasing day by day. These Electronic converters and loads are the sources of harmonics and reactive power. Also the presence of single-phase loads in the 3-phase distribution systems causes many problems in the distribution and transmission systems. This is because of the unbalanced current drawn by the unbalanced loads. These two problems greatly affect the performance of the power system network, and reduce the system power quality.
Due to the rapid development in power electronic devices and state-of-the-art electronic circuit technology, the active power filters (APFs) have been developed and put into practical applications. The APF can solve problems of harmonic and reactive power simultaneously. APF can also be used to compensate the unbalance in the threephase load currents and make the grid supply only the positive-sequence components of the load currents.
APFs are still expensive due to high switching operation of its switches. Many efforts are done in recent years to reduce the number of the APF switches from six switches to four switches. This reduces the overall cost of APF, but DC-link of APF must be modified by splitting the capacitor into two capacitors, and the capacitor MidPoint acts as the third leg of the inverter. And then the different control schemes must be also modified to control the two DC-link capacitor voltages through controlling only four-switch inverter.
This thesis is mainly divided into two main sections. The first section introduces a four-switch three-phase shunt APF (FSTP-APF) based on one cycle control (OCC) technique for compensating the currents of non-linear 3-phase loads. The power stage of FSTP-APF uses only four semiconducting switches which lead to reduce the overall cost of APF. The proposed technique retains the advantages of the conventional OCC, such as no reference current calculation, no need to use phase-locked loop (PLL), very simple control circuit and constant switching frequency. In addition the modification reduces the number of semiconductor switches, and the filter output inductances also reduces the number of sensors to only four sensors, two of them for measuring supply currents and the others for measuring DC-link voltages, and the control algorithm becomes simpler. The feasibility and performance of the proposed technique are demonstrated through the simulation and experimental verifications.
The power stage of shunt APF used to compensate non-linear unbalanced 3phase loads is of two types; Four-leg APF and Spilt capacitor APF.
The second section introduces a split-capacitor APF based on synchronous reference frame theory (SRF) for compensating the currents of 3-phase 4-wire unbalanced non-linear loads. Two modifications are done in reference currents calculations using SRF. The first one is to modify the DC-link voltage control loop to control two voltages across two capacitors on the DC-link; this is done to make them constants at a certain value for the correct operation. The second one is that the SRF zero-sequence current is included in reference currents calculation to compensate the unbalance in currents in the supply side. The current controller used is the hysteresis current control due to its simplicity and fast response in controlling the filter currents. The advantages of the modification are to make the supply see the unbalanced nonlinear load with Shunt APF as a linear balanced load at point of common coupling (PCC), and the current controller becomes simpler containing only three current loops, and lower number of sensors and semiconductor switches are used. The mathematical analysis is done to modify the DC-link voltage control. The system performance is verified through simulation studies using MATLAB/SIMULINK. An experimental setup is implemented to validate the system performance actually.