Power Control in AC Isolated Microgrids with Renewable Energy Sources and Energy Storage Systems

Transcription

1 Power Control in AC Isolated Microgrids with Renewable Energy Sources and Energy Storage Systems Abstract Introduction: The supply of electricity to these communities in several developing countries, in general, is still done in a precarious way using diesel generator that operates for 3 4 h a day. This has happened mostly due to the high cost associated with the expansion of the conventional power grid to these communities. In some cases, technical and environmental constraints also have been factors that have prevented the full electrical service in these communities, particularly those located on oceanic islands. Another application of isolated microgrids occurs when a microgrid is disconnected from the main grid for any reason, in general to improve the local energy reliability. Due to the intermittent nature of renewable energy sources (RESs), the uninterrupted availability of the generation system, and its stand-alone operation, it is required some kind of energy storage system (ESS) in these applications. Although there are several different ESSs, in practical applications, battery banks have been used mainly due to economic reasons. In general, a backup

2 energy source must be used during the lack of the primary renewable energy sources, when the ESS is discharged or when the generation system is under maintenance. Existing system: A crucial issue related to these autonomous and distributed microgrids is to control the power generated internally to maintain the system energy balance in order to keep the terminal voltage of the battery bank limited to a safe value and consequently maintain its state of charge (SOC) under control. One possible solution is to use centralized or distributed resistive dump loads to burn the eventual excess of generated power, is presented. Another possibility is to use physical communication (wiring) between the converters to inform their control systems about the balance of energy in the microgrid and the amount of power that each of them must generate to keep this energy balance under control. Proposed system: This paper proposes an alternative strategy to control the generated power within an isolated ac microgrid with distributed RES. The proposal is to control the terminal voltage of the

3 existing battery banks below or equal its maximum allowable value. This is done by limiting the amount of power that each energy source can generate at each instant. The microgrid frequency is used to characterize the state of charge of the battery bank and quantify to the converters control systems how much power they need or can generate to maintain under control the internal power balance of the microgrid. The control of the battery banks terminal voltage implies indirectly the control of their SOC.

4 Applications: Grid connected applications Block diagram: INPUT DC SUPPLY DC TO DC CONVERTER THREE PHASE LOAD WIND AC SUPPLY TURBINE SIDE DC LINK GRID SIDE GATE DRIVER 12 V DC PIC CONTROLLER Copyright WITH 2015 BUFFER LeMeniz Infotech. All rights reserved 5 V DC

5 Tools and software used: MPLAB microcontroller programming. ORCAD circuit layout. MATLAB/Simulink Simulation.