Proportional–integral controller based small-signal analysis of hybrid distributed generation systems

The large band variation in the wind speed and unpredictable solar radiation causes remarkable fluctuations of output power in offshore wind and photovoltaic system respectively, which leads to large deviation in the system frequency. In this context, to minimize the deviation in frequency, this paper presents integration of different energy resources like offshore wind, photovoltaic (PV), fuel cell (FC) and diesel engine generator (DEG) along with the energy storage elements like flywheel energy storage system (FESS) and battery energy storage system (BESS). Further ultracapacitor (UC) as an alternative energy storage element and proportional–integral (PI) controller is addressed in order to achieve improvements in the deviation of frequency profiles. A comparative assessment of frequency deviation for different hybrid systems is also carried out in the presence of high-voltage direct current (HVDC) link and high-voltage alternating current (HVAC) line. Frequency deviation for different isolated hybrid systems are presented graphically as well as in terms of integral square error (ISE). Both qualitative and quantitative analysis reflects the improvements in frequency deviation profiles with use of ultracapacitor (UC) as energy storage element.