Reactive power compensation using D-STATCOM with fuzzy logic supervision

In a power system, switching on/off of large inductive loads causes a drop/rise in the voltage at the load bus due to increase/decrease in reactive VAR demand which may lead to voltage instability. Additionally, three-phase, four-wire distribution systems faces poor power quality problems such as unbalanced loading, excessive neutral current and voltage distortion due to current harmonics. In order to keep the voltage within a limit and mitigate such power quality problems, reactive power compensation devices such as distribution static compensator (DSTATCOM) are used as custom power devices which help in increasing the operational efficiency and reliability of power distribution systems. In a D-STATCOM, generally, the DC link capacitor voltage is regulated using a proportional integral (PI) controller along with various control algorithms used for load compensation. However, during load changes, there is considerable variation in DC link capacitor voltage which might affect compensation. In this paper, a fuzzy logic based supervisory method is presented to improve transient performance of the DC link. A mamdani fuzzy logic based controller is designed in such a way that the gains generated by the fuzzy supervisor are added to the reference proportional and integral gains of the PI controller which helps to maintain the DC Link voltage. A MATLAB/Simulink model for the system with a resistive inductive (R-L) load is developed using SimPower Toolbox. It is observed that the fuzzy logic supervised D-STATCOM successfully compensates for the reactive power required by the load. A transient (load throw off condition) is created by removing one of the phases of the load for a short duration. The DC link capacitor voltage is observed and compared to a case when only a conventional PI controller is used with no fuzzy supervision. It is observed that the proposed controller has a better performance than the conventional one in terms of better voltage regulation and faster settling time.