Speed control of synchronous machine by changing duty cycle of DC/DC buck converter

Global Conference on Energy and Sustainable Development, 2015-02-24, 2015-04-26, Coventry, UKRenewable energies such as wind or solar energy are naturally intermittent and can create technical challenges to interconnected grid in particular with high integration amounts. In addition, if wind or solar is used to supply power to a stand-alone system, continuous power supply will be met only if sufficient energy storage system is available. The global penetration of renewable energy in power systems is increasing rapidly especially wind and solar photovoltaic (PV) systems. Hybrid wind and solar PV generation system becomes very attractive solution in particular for stand-alone applications. It can provide better reliability since the weakness of one system could be complemented by the strength of the other one. When wind energy is integrated into grid, maximum power point tracking control could be used to optimize the output of wind turbine. In variable speed wind turbine, the turbine speed is varied according to the wind speed. This paper presents a comparison between two methods of controlling the speed of a wind turbine in a microgrid namely; Proportional-Integral (PI) control of the tip speed ratio and stored power curve. The PI method provides more controllability, but it requires an anemometer to measure the wind speed. The stored power curve method, however, is easier to implement, but the amount of energy extracted can be less. The system has been modelled using Matlab/Simulink.The work is financially supported by the Government of Oman, which provides a PhD grant for Rashid Al Badwawi. Also, financial support from EPSRC-DST funded RESCUES project (EP/K03619X/1)

Power management of AC islanded microgrids using fuzzy logic

In an islanded AC microgrid consisting of renewable energy sources, battery, and load, the battery balances the difference between power generated by renewable sources and that consumed by the load. However, battery charging capacity is limited and its state of charge needs to be maintained within the safety limits. Furthermore, battery has limited maximum charging and discharging power. This paper proposes a controller based on fuzzy logic to prevent the battery state of charge and charging/discharging power from exceeding their limits regardless of variations in load and intermittent power of renewable sources. The microgrid considered in this paper consists of PV, battery, load and auxiliary supplementary unit. The fuzzy logic controller alters the AC bus frequency which is used by the local controllers of the parallel units to curtail the power generated by PV or to supplement power from the auxiliary unit. The main merits of the proposed controller are simplicity and easiness of implementation without the need for any communication links between the parallel units. Matlab/Simulink results are presented to validate the performance of the proposed controller