Micro-grid Frequency Regulation In Islanded Mode

Micro-Grid is getting more significance because of their ability to increase renewable penetration in current power system.MG provides a substantial solution to keep power supply load demand balance.In islanded condition,due to the loss of support from large power grid,the frequency instability problem of the microgrid is more prominent.Thus controlling this frequency deviation of the microgrid has become an urgent problem to be solved.This thesis mainly designs a coordinated control architecture of active and reactive power(PQ)suitable batteries(BESS),DC-link voltage control for PV system along with primary frequency droop control and secondary distributed control for islanded microgrid.This thesis first proposes the overall architecture of control system suitable for islanding microgrid is proposed which includes first-level droop control and second level correction control.Firstly,a primary speed dispatch control method based on PQ control theory is proposed,and a compound loop controller is designed which consist of voltage source converter(VSC),outer power loop controller and inner current loop controller.In this proposed work,PI controller is chosen as hardware element of both inner and outer loop controllers.The controller requires no extra communication structure.This work generates reference currents based on outer power controller,which then become input of inner current controller and is introduced into the PI control to eliminate frequency deviation.The inner current controller is designed to have high bandwidth to give speed response while PQ control generates required active power to feed the load.BESS shows fastest response to power change so in case of load/power variation or islanding,it provides power with primary frequency control.In secondary control,diesel generator operates,replacing the Battery and take control of supplying active and reactive power to the load.Once the generator comes online,the BESS stops power injection/absorption and goes into standby mode.In this thesis,it is also checked for the battery not to absorb active and reactive power and does not act like a load.In this regard the reference power signal provided to the VSC of BESS must become zero when generator turns ON.Simulation results show that the control strategy designed in this thesis can realize the effectiveness of frequency control of MG in the islanded mode,and the microgrid operation has better flexibility.