Research Of Seamless Transfer Control Strategy Of WTG-PV-Diesel-BESS Hybrid Power Plants System

Hybrid power plants, which are composed of diesel generators, battery energystorage system(BESS) and renewable energy resources such as wind turbinegenerator(WTG) and photovoltaic(PV), not only can take advantage of wind and solarpower to increase economic and social benefits, but also can improve power supplyreliability and stability of the micro gird. With the number of engineering applicationsand installed capacity of hybrid power plants system gradually increased, the controlstrategy has become a very critical part. Micro grid has two typical working modes:grid-connected mode and islanded mode. The transfer between these two modes shouldbe seamless.The transfer control strategies of WTG-PV-Diesel-BESS hybrid power plantssystem(WPDBHPS) include the followings:According to analyzing the structure of WPDBHPS and its components, this paperhas maken models of WTG, PV, BESS, diesel and loads with DIgSILENT software.This paper has designed the control strategy and energy control algorithm of WPDBHPbased on the characteristics of grid-connected mode and islanded mode of WPDBHPS.WPDBHPS has two restrictions:one is that not allow power to flow from themicrogrid to the gird, the other one is that ensure the power supply demand of importantloads as much as possible. This paper focuses on seamless thansfer betweengrid-connected mode and islanded mode of WPDBHPS under these two restrictions.When grid is failure, WPDBHPS is disconnected from grid. According to several energysupply and demand situations between distributed generations and loads, disconnectingfrom grid is divided into two situations: bess or diesel is the single master distributedgeneration, both of bess and diesel are the main distributed generations simultaneously.When grid is back to normal, WPDBHPS should be able to timely detect and reconnectto grid as soon as possible. Considering the time of control method changing andbreaker off is difficult to synchronize, this paper has designed the grid reconnectioncontrol strategy in case of the deviation of voltage amplitude, frequency and the phasebetween WPDBHPS and grid. The simulation results show that transfer control strategies of WPDBHPS arecorrect and reliable. These control strategies can achieve the control objectives on thetwo major issues: disconnected from grid and reconnected to grid.