Minimization of Total Harmonic Distortion for Long Transmission Lines using PI Controller

Development of power electronics based devices help to improve transmission loss and increase the power transfer capability of power system. Parameters like voltage, real and reactive power flow can be controlled by using FACTS devices in transmission lines. . Power sources act as non linear loads, drawing a distorted waveform that contains harmonics. These harmonics can cause problems ranging from telephone transmission interference to degradation of conductors and insulating material in motors and transformers. Therefore it is important to gauge the total effect of these harmonics. The summation of all harmonics in a system is known as total harmonic distortion (THD). Harmonic Distortion is the degree to which a waveform deviates from its pure sinusoidal form. Shunt Flexible AC Transmission System (FACTS) devices such as SVC and STATCOM, when placed at the midpoint of a long transmission line, play an important role in controlling the reactive power flow to the power network and hence both the system voltage fluctuations and transient stability. A three phase transmission system has been studied first without using any compensating devices. The voltage and current waveform of the uncompensated system has been observed. Then the system is studied with the connection of compensating device STATCOM in parallel with the system at the middle end of the transmission line. The STATCOM consists of Voltage Source Converter fed by a dc reference voltage. The pulses to be given to the converter are fed from the PI Controller, which compares the system voltage with the reference voltage and produces the necessary error signal. Results has been shown through MATLAB Simulink