Positive sequence ISCT based distribution static compensator for non-stiff source using state feedback control

This paper proposes positive sequence extraction based state feedback theory for neutral clamped voltage source inverter (VSI) based Distribution Static Compensator (D-STATCOM) for three phase, four wire, non-stiff system. Generally, in stiff system, the instantaneous symmetrical component theory is used to generate the reference compensator currents. However, this is not useful directly in non-stiff systems. In order to improve the compensator performance for non-stiff source and to achieve desired load compensation, positive sequence extraction based state feedback using Linear Quadratic Regulator (LQR) is proposed. The switching sequence for VSI is generated using hysteresis current control (HCC) technique and for effectively nullifying the high frequency switching components from terminal voltages and source currents, shunt filter capacitors are used. The results are verified for unbalanced and nonlinear load condition. The proposed theory gives desired load compensation with the undistorted terminal voltages under balanced source conditions. The results are extracted using extensive digital simulations performed in MATLAB/SIMULINK environment.