Direct nonlinear control for individual DC voltage balancing in cascaded multilevel DSTATCOM

The need for improving the performance of the distribution static compensator (DSTATCOM) is sensed more and more due to the importance of the system power quality. Hence, in this paper, one of the nonlinear control methods which is named exact linearization via feedback in DSTATCOM application is developed. In this new multiple input multiple output (MIMO) control method, V_dc and i_q are controlled and the capacitor voltage, unlike the other control methods, is directly regulated. The result will be a fixed V_dc equal to the reference value and there is possibility of controlling all capacitors in multilevel inverters independently and removing the PI controller from the system. Thus, operating point can be simply changed without regulating K_p and k_I again. To compare the proposed control scheme with the conventional methods, implemented in multilevel DSTATCOM, different reasons causing unbalanced voltages in the capacitors, such as different capacitor´s initial charges, different reference voltage values, different capacitances and a combination of the mentioned reasons are studied. Averaged model method is used for simulation of the system, using MATLAB/Simulink software. The results show the effectiveness of the proposed method in controlling individual capacitor voltages.