Performance optimization of AC-DC bus tie line bidirectional converter for microgrid applications

COEP-Microgrid, project by the students of College of Engineering, Pune aims at establishing a microgrid in the college campus serving as a living laboratory for research and development of novel grid technologies. Proposed microgrid has a DC bus connected to solar cells, fuel cells and battery while AC-bus connected to wind power plants, pico hydro plant, Static Synchronous Compensator (STATCOM), local AC loads and to the electricity grid with an islanding scheme. To operate the energy sources at the DC bus in parallel with the electric grid, DC-AC tie line converter, i.e. grid tie inverter is required. This paper thus aims at the description of the entire design and implementation of the bidirectional grid tie inverter used in proposed microgrid application. The bidirectional grid tie inverter has a 2 level VSI topology with Sine Pulse Width Modulation (SPWM) based control strategy. Along with the design, the paper describes the synchronization techniques of the inverter with the grid through phase, frequency and voltage control methods. The proposed scheme discusses about the problems regarding its practical implementation and various optimization techniques used to improve its performance.