Power Electronics Interfaces for RPower Electronics Interfaces for RPower Electronics Interfaces for R

D t tDepartmentDepartment

Introduction ConfigurationIntroduction ConfigurationgDistributed generation (DG) has gained great public interest as aDistributed generation (DG) has gained great public interest as al d ffi i t h t d l t i With dc micro socleaner and more efficient approach to produce electric power. With dc micro-so

Although they are frequently working with renewable energyAlthough they are frequently working with renewable energy(RES) h l i ll d i d bi h Single stage (dc ac)sources (RES), e.g. photovoltaic cells and wind turbines, they can Single-stage (dc-ac)

also be powered by other kinds of micro-sources e g fuel cells The inverter handles alalso be powered by other kinds of micro-sources, e.g. fuel cellstracking (MPPT) outputand micro-turbines. tracking (MPPT), outputHigher converter efficieng

DG units can be systematically organized into a microgrid, i.e. ay y g gtiny power system with a cluster of loads and distributed Two-stage (dc-dc and dtiny power system with a cluster of loads and distributed g (

The dc dc converter pergenerators operating together through an energy manager and The dc-dc converter perg p g g g gy gother control devices A microgrid can be ac or dc single phase or The inverter performs ouother control devices. A microgrid can be ac or dc, single-phase or p

Lower PV or fuel cell outhree-phase, and can be connected to low voltage or medium Lower PV or fuel cell oup gvoltage power distribution networksvoltage power distribution networks.

The DG units in a microgrid are interfaced by power electronicsThe DG units in a microgrid are interfaced by power electronicsconverters. With delicately designed converter control schemes, ay g ,microgrid can provide significant flexibility to fulfill customermicrogrid can provide significant flexibility to fulfill customerrequirements in terms of efficiency, security, reliability, powerq y, y, y, pquality etc This research project focuses on the configurationsquality, etc. This research project focuses on the configurations

Si l tand control of microgrid. Single-stg

Two-stagTwo stag

fA two-stage configisolation transformisolation transform

C t l f DGControl of DGControl of DGIllustrative diagram of the configuration of aIllustrative diagram of the configuration of a t i l i idtypical microgrid

Overviewyp g

OverviewPower management stragload demand matchingload demand matching,units, and they have diffe, y

In grid connectioIn grid-connectiog

Due to the presence of apmain task of DG controlmain task of DG controlreactive power output,Di f t i l l t i p p ,MPPT or the central powDiagram of a typical power electronics MPPT or the central powg y

interfaced DG system The task can be done thinterfaced DG system

Power flow controlPower flow control

Experimental prototype of DG systemsExperimental prototype of DG systemsPower flow control tPower flow control t

Renewable Energy Based MicrogridRenewable Energy Based MicrogridRenewable Energy Based Microgridgy g

Y i Li Yif i W d Ji i HYunwei Li, Yifei Wang and Jinwei HeYunwei Li, Yifei Wang and Jinwei Hef El t i l d C t E i i U i it f Alb tof Electrical and Computer Engineering, University of Albertaof Electrical and Computer Engineering, University of Alberta

ns of DG Interfacing Power Electronicsns of DG Interfacing Power Electronicsg

ources With non-utility-grade ac micro-sourcesources With non-utility-grade ac micro-sourcesTwo stage (dc dc and dc ac)Two-stage (dc-dc and dc-ac)

l tasks such as maximum power point Multi-stage (e.g. ac-dc, dc-dc and dc-ac)p pt voltage and current control

g ( g , )t voltage and current controlncyy

dc-ac))rforms MPPT and voltage boostrforms MPPT and voltage boost

T t fi tiutput voltage and current control

Two-stage configurationp g

tput voltage allowedtput voltage allowed

M lti t fi tiMulti-stage configuration

t fi titage configuration

ge configurationge configuration

A popular two-stage conversion topology for small wind turbine systemswind turbine systems

guration with energy storage and mermer

G I t f i P El t iG Interfacing Power ElectronicsG Interfacing Power Electronics

ategies of microgrid include real and reactive power control, frequency and voltage regulation, synchronization,g g p , q y g g , y ,etc These strategies are performed by properly controlling the interfacing power electronics converters of DGetc. These strategies are performed by properly controlling the interfacing power electronics converters of DGerent priority when the DG units are operated in either grid-connection or islanding modes.p y p g g

on operation In intentional islanding operationon operation In intentional islanding operationp g p

a stiff grid voltage, in this mode the When power outage of the main grid occurs, the microgridg g ,lers is to maintain desired real and

p g g , gmust be intentionally disconnected from the main gridlers is to maintain desired real and must be intentionally disconnected from the main grid.

according to the requirement of Each DG unit controller must be able to immediatelyg qwer management of the microgrid

ydetect this islanding situation Then they have to shedwer management of the microgrid. detect this islanding situation. Then they have to shed

rough current or voltage regulation. loads of less importance and properly share the powerg g g p p p y pdemand of the rest loads so as to maintain a constantdemand of the rest loads, so as to maintain a constantvoltage as well as a synchronized frequency, and helpg y q y, pcritical loads ride through the outage Furthermorecritical loads ride through the outage. Furthermore,advanced automatic load demand sharing schemes aregexpected to enable “plug and play” feature of DG units inexpected to enable plug-and-play feature of DG units inthe microgrid.e c og d

SP2PSP1PSP

*ω2PSP

*P *Pω1P 2P

ωthrough current regulation 1P 2P

ω through current regulation 1P 2

iωminω

PP max_2Pmax_1P

R l h i b t t DG it ith P dReal power sharing between two DG units with P-ω droop characteristicthrough voltage regulation characteristicthrough voltage regulation