Grid forming Battery Energy Storage System (BESS) for a highly unbalanced hybrid mini-grid

• A solution for highly unbalanced loads in hybrid mini-grid is proposed.
• A BESS based on per-phase dq control system with FAE is discussed.
• Zero error in steady-state with good transient response is achieved.
• BESS can supply power in one phase and absorb in the other two.
• Voltage is balanced for unbalanced, non-linear, motor and PV source.

Diesel hybrid autonomous power systems present good potential for remote communities. Fuel consumption and emissions can be reduced by the use of Renewable Energy Sources (RESs) such as photovoltaic (PV) and wind. With a Battery Energy Storage System (BESS), power generation and consumption can be decoupled allowing further reductions in fuel consumption. An interesting scenario is when the diesel genset can be shut down and the load is supplied by the RESs and BESS. In this case, the latter has to form the grid, regulating voltage and frequency, what can be very challenging under highly unbalanced loads and single-phase RESs. This paper discusses the use of per-phase dq control in a grid forming BESS that provides good dynamic and steady-state response. Experimental results on a laboratory test bench of a BESS interface providing regulated balanced voltages under various demanding load conditions are presented.