This presentation discuss about design and implementation of Microcontroller Based Power Management System for Standalone Micro grids with Hybrid Power Supply. 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 Fuel Cell
Fuel Cell 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
PMS is governed by following peculiarities. Maximum power provided by pv array is lower than maximum power absorbed by battery during charging phase. Fuel Cell is requested to operate when the system is disconnected from the external distribution system
Operating Modes of Fuel cell
- Grid Connected Operating Mode
- Islanded Operating Mode with Fuel cell in Operation
- Islanded Operating Mode with Fuel cell not in Operation
Battery State Of Charge Estimation
Estimation models depends upon five basic criteria. They are measurement of electrolyte specific gravity, battery current time integration, battery impedance /resistance estimation, measurement of battery open circuit voltage and models that take into account the electrolyte temperature, discharge, rate and other battery parameters.
Experimental Validation Of The State Of Charge 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
Fuel cell output is controlled in order to track a target SOC value. 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 and Minimize the number of FC start-up and shut down manoeuvres.
PMS Implementation Into A Microcontroller
Fuel cell control is implemented into a real time microcontroller equipped with an FPGA. Microcontroller runs for four main cycles. They are Data acquisition that calculates microgrid electrical state variables, Data acquisition that determine the Fuel cell status, SOC estimation and Fuel cell set point control. 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 Fuel cell.