1. A Microcontroller Based Power Management System for Standalone Micro grids With Hybrid Power Supply1

2. 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

4. PEM FC

5. 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

7. 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

8. OPERATING MODES OF FC

9. Cont.…

11. 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

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

13. Cont.…

15. 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

17. 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

18. Intervals defining FC in operation

19. Cont.

22. 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

23. 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