Reconfigurable Grid Following/Grid Forming Control based Photovoltaic Multilevel Inverter for Grid Stability Support

This paper introduces an adaptive reconfigurable grid following (GFL)/grid forming (GFM) control technique for a photovoltaic (PV) multilevel inverter which is connected to a renewable energy source (RES) dominant lower inertia grid. An asymmetric cascaded H-bridge (CHB) based multilevel inverter with binary asymmetry ratio is considered for the PV inverter in this work. This inverter topology has minimum isolated DC voltage source count requiring one PV source for supplying DC link of only one isolated H-bridge cell in each phase and the remaining DC links of the H-bridge cells are connected to floating capacitors which have natural balancing capability. The control structure for the inverter has the ability to transit flexibly between GFL and GFM control modes emulating their individual characteristics. Furthermore, an adaptive reconfiguration control technique is proposed which optimally controls the inverter between GFL and GFM control modes when any contingency event is detected. The proposed adaptive reconfiguration controlled inverter is simulated in MATLAB/Simulink environment to investigate the system performance under frequency based contingency events. A comparative study between different control methods is also implemented which establishes the superiority of the proposed adaptive control.