Reactive Power Compensation in Distribution Grids: An Application of Trinary Cascaded H-bridge Multilevel Inverter

Recently, application of multilevel inverters (MLIs) in reactive power compensators has achieved remarkable attention. This paper presents a model predictive control (MPC) method for distribution grid static synchronous compensator (DSTATCOM) based on trinary cascaded H-bridge (T-CHB) MLI. The T-CHB consists of the cascaded connection of H-bridge cells with trinary dc voltages. T-CHB produces the higher number of output voltage levels with a lower number of power switches compared to the several alternative MLIs. The main challenge in application of T-CHB as DSTATCOM is controlling the voltages of capacitors in unequal voltage levels. This paper proposes a modified finite-set MPC method to achieve this goal. Through a multi-objective optimization, the compensated reactive current and voltages of capacitor are kept under control. Also, the switching frequency of the high-voltage cell is added to the optimization process to mitigate the switching losses in that cell. Simulation results in MATLAB/SIMULINK are presented to validate the performance of T-CHB DSTATCOM.