Dr. Gamal Mohamed Abdelrahman Sarhan :: Publications:

Inverter-based distributed generators (DGs) can be operated in parallel comprising an isolated microgrid or connected to the main power system. In the first case there must be an advanced control system to adjust frequency and power sharing between inverters constituting the microgrid. In grid mode the DGs inject electrical power to grid without any contribution to rotating inertia that give the power system its distinctive stability characteristics and conventional control liability. Improvement to DGs by the relatively new control methods based on virtual synchronous generator (VSG) and synchronverter (SV) have been suggested to control such DGs to emulate conventional synchronous generator. By these methods a controlled amount of virtual inertia can be injected in mains besides load sharing. This paper suggests a control method of such systems based on direct control of power angle between inverter voltage and grid voltage. In this method the grid phase angle is directly computed from the grid 3-phase voltages without phased locked loop (PLL) or other synchronization methods. A linearized small signal model of power angle is used to implement this control method. The model can also emulate rotating inertia, injecting a controllable amount of energy into grid during frequency transients to enhance transient stability. Damping effect of damper bars is taken into account in model and proves to be effective in damping out oscillations.