Power balancing in autonomous micro grid with variable speed pump

This paper presents a method for supply-demand balancing in autonomous micro-grids using a variable speed pump. The pump is driven by a wound rotor induction motor (WRIM) utilizing a slip power recovery control. The slip power from the rotor is recovered through a line-commutated inverter, which gives the capability for the motor to obtain variable speed operation. Power drawn by the pump being proportional to cube of the speed, the stator power is varied over a wide range as the speed is varied. A load frequency controller senses the deviation in the micro-grid frequency due to the supply-demand mismatch and it suggests the triggering angle of the inverter. This makes the power drawn by the pump track the load variation, so as to nullify the frequency drift and restores the power balance in the micro-grid. A 250kW WRIM is used to drive the proposed micro-grid, which has a maximum demand of 250 kW. The entire system is simulated in MATLAB/Simulink and the variable speed operation of the pump is demonstrated for different triggering angles of the inverter.