Frequency Control in a Microgrid System considering Time Delay and Parametric Uncertainties

Abstract

A microgrid (MG) can be formed by interconnecting power generating sources like newlineWind Turbine Generators (WTG), Photo Voltaic (PV) systems, Diesel Generators (DG), Fuel Cells (FC), Battery Energy Storage Systems (BESS) in an AC distribution system. The MG is so constructed, that it can be operated in an islanded mode located closer to load centers. One of the major issues in the operation of an islanded MG is the frequency deviation caused by power generated from non dispatchable renewable energy sources (RES) like wind and PV. When the power generated from RES varies, other dispatchable power sources (DG, FC and BESS) can be controlled to supply the specified load demand. The critical issue with respect to the frequency regulation of MG is the time delay which is due to the communication network between the Microsource Controller (MC), and Micro Grid Central Controller (MGCC). When the load demand is set in a MG, MC communicates with MGCC. The MGCC provides real power set points to the MC.PI controllers are normally implemented with each MC to improve the frequency newlineregulation in MG s. The present research deals with the computation of PI controller newlineparameters for the islanded MG considering the communication time delays. The time delays (TD) considerably affect the frequency of MG. Hence, it is necessary to consider the TD while designing the PI (Proportional and Integral) controller for the MG system. For the proper design of PI controllers, a suitable method has to be adopted. In this regard, D-partition method (DPM) is used to find PI controllers from the D-curve. By using the controller and the system transfer function, Kp and Ki equations are formed. Replacing s = j! in the Kp and Ki equations, D-curve is drawn for various values of !. D-curve consists of all stable PI values which are derived from the system and controller transfer function. Since, D-curve consists of many stable values of PI controller, it is impossible to obtain the exact value. By trial and error, the best PI controller parameters.