Reactive Power Compensation and Harmonic Mitigation in 25 kV AC Railway System Using Shunt Active Filter

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Addis Ababa University


The AC railway systems show typically poor power quality due to their inherent electrical load characteristics. The moving and non-linear load characteristics of the locomotives consume the large reactive power and produce high harmonic currents, so that the total power factor becomes adversely affected. These power quality problems in the AC railway system can constrain the amount of power delivered to the locomotive and have a negative effect on themselves as well as on the public grid. As a result, detailed study of reactive power and harmonic mitigation is required in traction substation. The thesis deals on compensating reactive power consumption and harmonic mitigation of 25 kV electrified railway system of Addis Ababa-Djibouti railway line as case study. The active power filters have gained much more attention because of their performance to mitigate the harmonics and reactive power issues. The performance of active filter depends upon the control theory that is employed to formulate the control algorithm of active filter and controller of the active filter is the key and heart of the filter which greatly affects its performance. So, design of shunt active filter to mitigate the harmonics and reactive power problems with controller based on Synchronous (d-q) reference frame theory is the core area of this work. MATLAB/Simpower computer simulation is used as a simulation tool for the thesis. When the Shunt Active Power Filter is connected to the system, we can observe from the simulation result that THD of load current has reduced from 20.5% to 4.6% which is below 5% the harmonics limit imposed by IEEE 519 standard. The reactive power demand is reduced to nearly zero value, the power factor and pantograph voltage of traction system also improved. Thus, the simulation results after implementing the proposed filter shows that shunt active power filter can effectively compensate reactive power and harmonics.



Shunt Active Power Filter, Reactive Power, Harmonics, Synchronous Reference Frame Theory Control