A Microcontroller Based Power Management System for Standalone Micro grids With Hybrid Power Supply 1

INTRODUCTION DISTRIBUTED generation result in enhanced continuity of service and in increased customer participation to the electricity market. By allowing the network to operate in islanded conditions these opportunities can be achieved Fuel cells provide clean and silent operation, cost effective supply of power

PEM FC

DESCRIPTION OF PEM FC FC stack is fed by hydrogen from anode Pressure reducing valve reduces the inlet pressure to 1.8 bar Two electro valves are placed at inlet and outlet -safety valve and outlet end valve Air mass flow is provided by blower at cathode Gas to gas porous membrane at humidifier ensures adequate water supply Three way valve at the outlet controls the water temperature

FUNCTIONS OF AUTOMATIC PMS Functions of PMS is governed by following peculiarities maximum power provided by pv array is lower than maximum power absorbed by battery during charging phase Fc is requested to operate when the system is disconnected from the external distribution system

OPERATING MODES OF FC

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BATTERY STATE OF CHARGE ESTIMATION Estimation models depends upon five basic criteria 1.measurement of electrolyte specific gravity 2.battery current time integration 3.battery impedance /resistance estimation 4.measurement of battery open circuit voltage 5.models that take into account the electrolyte temperature, discharge, rate and other battery parameters

Cont. The equation summarizes the methods 2, 4, 5 where

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EXPERIMENTAL VALIDATION OF THE SOC ESTIMATION Initial battery SOC is adjusted to 50% Then microgrid is activated in variable load profiles The test is stopped when predefined final estimate value is reached Different test is performed for values 30%, 40%,50%,60% At end of each test battery is disconnected and discharged with a constant rate

CONTROL STRATEGY AND LIMITERS OF THE BATTERY VOLTAGE FC output is controlled in order to track a target SOC value,SOC* SOC* is predetermined as an average SOC level allowing us to:- Keep the storage system in a state that is able to supply energy in case of load request or receive energy in case of positive net power produced by PV Minimize the number of FC start-up and shut down manoeuvres

Intervals defining FC in operation

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PMS IMPLEMENTATION INTO A MICROCONTROLLER FC control is implemented into a real time microcontroller equipped with an FPGA Microcontroller runs for four main cycles Data acquisition that calculates microgrid electrical state variables Data acquisition that determinethe FC status SOC estimation FC set point control

Cont. Cycle #1 processes microgrid electrical variables These variables are shared with cycle #3 and cycle #4 for microgrid control state Cycle #2 is responsible for determining the status of FC