Fuel cell grid interconnection

Tennesse Technological University 1

MODELING/SIMULATION OF COMBINED PEM FUEL CELL AND MICROTURBINE DISTRIBUTED GENERATION PLANT

Rekha .T. Jagaduri

Department of Electrical and Computer EngineeringTennessee Technological University


OUTLINE

Overview of Distributed Generation Plant. Micro turbine as a DG. PEM Fuel Cell as a DG. Modeling of micro turbine. Modeling of fuel cell. Control Systems of micro turbine and fuel cell. Grid connected micro turbine and fuel cell. Simulation results. Conclusion. Future work.


OVERVIEW OF A DISTRIBUTED GENERATION

Distributed Generation (DG) is the use of small-scale power generation technologies located close to the load being served.

It includes, for example, photovoltaic systems, fuel cells, natural gas engines, industrial turbines, micro turbines, energy-storage devices, wind turbines, and concentrating solar power collectors.

These technologies can meet a variety of consumer energy needs including continuous power, backup power, remote power, and peak shaving.

They can be installed directly on the consumer’s premise or located nearby in district energy systems, power parks, and mini-grids.


ECONOMIC ADVANTAGES OF DG

Economic advantages include one or more of the following: Load management Reliability Power quality Fuel flexibility Cogeneration Deferred or reduced T&D investment or charge Increased distribution grid reliability/stability


MICRO TURBINE AS A DG

Micro turbine made its commercial debut in 1998. Micro turbines belongs to an emerging class of small-scale distributed

power generation Basic components: compressor, combustor, turbine, and generator. Typically in the 30-400 kW size.


MICRO TURBINE


MODELING OF MICRO TURBINE

Mechanical Equations:

Electrical Equations:

ElectricalEquations

MechanicalEquations

Pm

Vf

Pe

meo

PPDdtd

fH

qqdd

ddqq

IXrIV

IXrIVE

0

''

fdddddo EIXXEdtdET )'('''

0

dtd


TWO AXIS MODEL OF A MICRO TURBINE

Phasor diagram of Micro turbine


MICRO TURBINE CONTROLS

Overall block diagram of Micro turbine control

EXCITEREXCITER

AVR

GOVERNOR

TURBINEPref

Vref

Vt

GENERATOR


FREQUENCY CONTROL OF MICRO TURBINE

GOVERNOR TURBINE

1R

refmP ,

mPmP

moP

-

+ +

+

Frequency control block


VOLTAGE CONTROL OF MICRO TURBINE

refoV

trefV

AMPLIFIER EXCITER

tV

eVrefV+

+

+

-

FV

Voltage control block


FUEL CELL AS A DG

First fuel cell was developed in 1839 by Sir William Grove. Practical use started in 1960’s when NASA installed this technology to

generate electricity on Gemini and Apollo spacecraft. Types of fuel cells: phosphoric acid, proton exchange membrane, molten

carbonate, solid oxide, alkaline, and direct methanol. Typically 5-1000+ kW in size, A number of companies are close to commercializing proton exchange

membrane fuel cells, with marketplace introductions expected soon.


BASIC PRINCIPLE OF A FUEL CELL

A fuel cell consists of two electrodes separated by an electrolyte. Hydrogen fuel is fed into the anode of the fuel cell. Oxygen (or air) enters

the fuel cell through the cathode. With the aid of a catalyst, the hydrogen atom splits into a proton (H+) and

an electron. The proton passes through the electrolyte to the cathode and the electrons travel in an external circuit.

As the electrons flow through an external circuit connected as a load they create a DC current. At the cathode, protons combine with hydrogen and oxygen, producing water and heat.

Fuel cells have very low levels of NOx and CO emissions because the power conversion is an electrochemical process.


PEM FUEL CELL

Anode side reaction: H2 2H+ + 2e-

Cathode side reaction: 0.5O2+2H++2e-H20 +Heat

------------------------------------Overall reaction: H2 + 0.5O2 H20 +Heat


OVERALL CHEMICAL REACTION OF PEMFC

Component balance Equation

Energy balance Equation

Nernst Equation

iOuti

ini

iS RWWdtdxT

RTPV

lossesgenerateds

sss

ss QQdtdCTM

dtdTCM

lossesOH

OHSocellFC E

xxx

FRTENV ]ln4

[ 22

22

2


POWER CONDITIONING UNIT

AC Voltage of the fuel cell: Vac = m . VFC where m is the modulation index, is the firing angle

Block diagram of fuel cell with PCU

INVERTER GRID

BATTERYINTERFACE

BATTERY

GRID

BATTERYINTERFACE

PCUFUELCELL


FUEL CELL CONTROLS

Power Control scheme

reffcP ,

o

-

+ +

+

PICONTROLLER

actualfcP ,


FUEL CELL CONTROLS

Voltage Control Scheme

PICONTROLLER

reffcV , m m

om

-

+ +

+

actualfcV ,


INTERFACING DG WITH POWER GRID

im

re

d

q

VV

V

V

cossin

sincos

The machine side characteristics of micro turbine are transformed to the system side frame of reference using the transformation matrix

The current injected into the system I = Y. V

Which could be further written as

Ire+ jIim = (G + jB). Vre + jVim


NUMERICAL ANALYSIS

Test System

FUELCELL

jXgt

jXfc

jXLNMICRO

TURBINE

POWERSYSTEM

SLD=PLD+jQLD

ZLD


CASE STUDY

Case 1: Assuming 10% increase in input power of the micro turbine

Case 2: Assuming 20% increase in input power of the fuel cell

Case 3: Assuming a 10% increase in micro turbine power (with and without governor)

Case 4: Assuming a 1% increase in micro turbine voltage reference ( with and without voltage regulator)


SIMULATION RESULTS – CASE 1








CONCLUSION

A combined micro turbine and PEM fuel cell plant connected to a power system was modeled and simulated.

Both the fuel cell and micro-turbine were assumed to be equipped with power and voltage control loops.

The micro-turbine was modeled using the d-q frame of reference and it was interfaced with the power system using transformation between this frame of reference and the system frame of reference.

A test system with typical numerical values was used to determine the accuracy of the model.


FUTURE WORK

The same procedure may be extended to the case of several DG’s connected to a power system.


THANK YOU

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Fuel cell grid interconnection