En 647 Distributed Generation and Microgrids

7/27/2019 En 647 Distributed Generation and Microgrids

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EN 647 DISTRIBUTED

GENERATION AND MICROGRIDS1


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CONTROL OFACTIVE AND REACTIVE

POWER

| The flows of active and reactive ower in a

transmission network are fairly independenty P is closely related to frequency

y s c ose y re a e o vo age

| Interconnected system with two or more

inde endentl controlled areas

y Control of frequency

y Maintain scheduled power interchange

y n erconnec e sys em w wo or moreindependently controlled areas

| Control of generation and frequency is known as

load frequency control (LFC) 2


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SPEED GOVERNING MECHANISM

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FREQUENCYDEPENDENCE OF A

COMPOSITE LOAD

| The fre uenc de endence of com osite load is

expressed asrLe DPP +=

y D is load damping coefficient expressed as % change

in load for 1% change in frequency.

y Load may be frequency dependent or independent

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PROBLEM -1 NO SPEED GOVERNING

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ISOCHRONOUS GOVERNOR

| Constant s eed

| Isochronous governor adjusts the turbinevalve/gate to bring the frequency back to the

nom na or sc e u e va ue.

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| Increase in load results in fre uenc deca at a

rate determined by the inertia of the rotor|As speed drops, Pm begins to increase and hence

re uces e ra e a w c spee s re uc ng

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| It works satisfactoril when enerator is

supplying isolated load| Only one generator in multi-gen system is

requ re o respon

| Isochronous generators cannot be used with two

or more units connected to the same s stem

y Each tries to control the system frequency to its

setting

| s goo o prov e roop c arac er s c oasharing is expected between generators

y Speed drops as the load is increased8


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GENERATORS WITH DROOP

CHARACTERISTIC

| Governor with State feedback

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DROOP

| Defintion: The ratio of s eed deviation or

frequency deviation to change in valve/gateposition or power output

| roop or regu a on means a requency

deviation causes 100% change in valve position or

power output

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LOAD SHARING BY PARALLEL GENERATORS

| Fre uenc is uni ue when the share a load

change' fPPP

==

1R

' f==2

R

21RP

=

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Amount of load picked up by each unit

depends on droop characteristic11

If % of regulation of units is nearly equal, the

change in the output of each unit will benearly in proportion to its rating


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LOAD SHARING BYPARALLEL

GENERATORS

| There is a steady state error associated with loadsharing

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CHANGING GENERATOR OUTPUT

| The relationship between speed and load is adjustedby changing an input reference

y Load reference set point

| When operating in parallel

y The output of each unit at any given system frequency canbe varied only by changing LRSP.

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LOAD REFERENCE SET POINT

| enera or connec e o ower ys emy LRSP has minimum effect on frequency

y Depends on size of other generators

y LRSP adjusts frequency

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COMPOSITE LOAD AND GOVERNOR

CHARACTERISTIC

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PROBLEM-2 DEAD BAND SYSTEMS

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AGC IN ISOLATED POWER SYSTEMS

| No issue of interchan e ower

| Restore frequency|Addition of integral is sufficient for units of AGC

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AGC IN ISOLATED POWER SYSTEMS

| Su lementar control action is slower than

primary control| It acts after primary speed control stabilizes the

sys em requency

|AGC adjusts the LRSP to change output of

enerators to override the effect of com osite

frequency regulation characterisitc

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AGC IN INTERCONNECTED POWER

SYSTEMS

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INTERCONNECTED POWER SYSTEM

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TWO-AREA WITH SUPPLEMENTARY

CONTROL

| With and=B =By Only the supplementary control in area 1 will

respond to load change in area 1 and changesgeneration to bring ACE1 to zero

y The change is not observable in area 2

| With and in their respective areas

y 11 2=B 22 2=Bdeviation twice as fast.

y Generation picked up by area 2 will be backed off

(Beta)

y Results in degradation of the system frequency

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En 647 Distributed Generation and Microgrids