A Novel Five-Level Inverter Topology with Reactive Power Control for Grid-Connected PV System

Abstract

These days multilevel inverters are more popular for grid-connected photovoltaic (PV) systems due to their low cost and high efficiency, as they effectively reduce total harmonic distortion (THD) and electromagnetic interference which results in lower leakage current. Traditional multi-level inverters can only inject real power that cannot provide quality output power. A new international standard VDE-AR-N4105 states that for a grid tied inverter of power rating below 3.6SkVA, a power factor (P)F of 0.95 leading to 0.95 lagging should be achieved. So, in this paper the proposed five-level inverter topology for grid-tie PV is controlled using a reactive power control method that ensures higher efficiency while enhancing the stability of the system. The proposed closed loop reactive power control technique additionally provides the ability to inject reactive power into the system. In this proposed topology the reactive power flow standard of operation is explained in details in relation to the proposed multi-level inverter topology. To validate the accuracy of the theoretical analysis, the control technique was applied to the existing multi-level inverter topology and then has been simulated in MATLAB/Simulink software. Comparisons were done on the basis of using and not using PLL for the existing multilevel topology and it is found that, synchronization is achieved with current and voltage if PLL is used, as a result PF is maintained close to unity whereas without PLL the PF decreases. Moreover the five-level output provides a much better output and better PF then other existing topologies.