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INTEGRATION OF ENERGY SOURCES:

a) Parallelling power generatorsb) Voltage control

Josep BalcellsUPC- Grup TiegMayo de 2014

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Outline

Introduction Regulation of active power: Frequency control Regulation of voltage: Reactive power control Paralleling synchronous machines or converters Problems of integration:Power flow control Example in CIRCUTOR Voltage control with SVC

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Characteristics of synchronous generators / converters

Since the shaft speed , nr , is linked to the electrical frequency , fe as

Where p is the number of pairs of poles.

The power output from the generator is related to its frequency by the following eq.:

60pnf r

e =

Operating frequency of the system

Slope of curve, W/Hz

)( ffsP nlp −=

)/( HzWfPsp ∆

∆=

4

A similar relationship can be derived for the reactive power Q and terminal voltage VT. When adding a lagging load to a synchronous generator, its terminal voltage decreases. When adding a leading load to a synchronous generator, its terminal voltage increases.

The plot of terminal voltage vs. reactive power is not necessarily linear. Both the frequency vs.active power and terminal voltage vs. reactive power characteristics are important for parallel operations of generators.

When a generator is operating alone supplying the load:1. The real and reactive powers are the amounts demanded by the load.2. The governor of the prime mover controls the operating frequency of the system.3. The field current controls the terminal voltage of the power system.

Characteristics of synchronous generators / converters

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Operation of generators in parallel with large power systems

Often, when a synchronous generator is added to a power system, that system is so

large that one additional generator does not cause observable changes to the system.

A concept of an infinite bus is used to characterize such power systems.

An infinite bus is a power system that is so large that its voltage and frequency

do not vary regardless of how much real and reactive power is drawn from or supplied

to it.

The power-frequency and reactive power-voltage characteristics are:

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Consider adding a generator to an

infinite bus supplying a load. The

frequency and terminal voltage of all

machines must be the same.

Therefore, their power-frequency

and reactive power-voltage

characteristics can be plotted with a

common vertical axis.

Such plots are called sometimes as

house diagrams and allow the

aclculation of the active power PG

which will be provided by the new

generator being coupled to the

infinite bus.

Operation of generators in parallel with large power systems

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Operation of generators in parallel with large power systems

If the frequency of the generator is

increased after it is connected to the

infinite bus, the system frequency

cannot change and the power supplied

by the generator increases.

Notice that in a system where VT and field

current are constant, then|EA| (module)

stays constant . If we increase f , phase δincreases and therefore , EAsinδ (which is

proportional to the output power) increases.

If the frequency of the generator is further increased, power output from the

generator will be increased and at some point it may exceed the power consumed

by the load. This extra power will be forced to be consumed by the load.

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Operation of generators in parallel with large power systems

After the real power of the generator is adjusted to the desired value, the

generator will be operating at a slightly leading PF acting as a capacitor.

Adjusting the field current of the machine, it is possible to make it supply reactive

power Q to the system.

Summarizing, when the generator is operating in parallel to an infinite bus:

The frequency and terminal voltage of the generator are controlled by the system

to which it is connected.

The controller set point of the generator frequency controls the real power

supplied by the generator to the system.

The generator’s field current controls the reactive power supplied by the generator

to the system.

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Generators in parallel with other generators of the same size

When a generator is working alone, its real and reactive power are fixed and

determined by the load.

When a generator is connected to an infinite bus, its frequency and the terminal

voltage are constant and determined by a bus.

When two generators of the same size

are connected to the same load, the

sum of the real and reactive powers

supplied by the two generators must

equal the real and reactive powers

demanded by the load:

21

21

GGloadtot

GGloadtot

QQQQPPPP

+==+==

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Generators in parallel with other generators of the same size: P sharing

Since , when starting G2, the frequency of

G2 must be slightly higher than the system’s

frequency, the power-frequency diagram

right after G2 is connected to the system

will be as shown.

The frequency of G2 is next increased,

and its power-frequency diagram shifts

upwards. Since the total power supplied

to the load is constant, G2 starts

supplying more power and G1 starts

supplying less power and the system’s

frequency increases until the load

balance is reached.

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Generators in parallel with other generators of the same size: Q sharing

When two generators are operating together, an increase in frequency (governor set

point) on one of them:

Increases the system frequency.

Increases the real power supplied by that generator, while reducing the real power

supplied by the other one.

When two generators are operating

together, an increase in the field current

on one of them:

Increases the system terminal voltage.

Increases the reactive power supplied

by that generator, while reducing the

reactive power supplied by the other.

If the frequency-power curves of both generators are known, the powers supplied

by each generator and the resulting system frequency can be determined.

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Generators in parallel : Example

Example : Two generators are set to supply the

same load. Generator 1 has a no-load frequency

of 61.5 Hz and a slope sp1 of 1 MW/Hz.

Generator 2 has a no-load frequency of 61.0 Hz

and a slope sp2 of 1 MW/Hz. The two generators

are supplying a real load of 2.5 MW at 0.8 PF

lagging.

a) Find the system frequency and power supplied by each generator.

b) Assuming that an additional 1 MW load is attached to the power system, find the

new system frequency and powers supplied by each generator.

c) With the additional load attached (total load 3.5 MW), find the system frequency

and the generator powers, if the no-load frequency of G2 is increased by 0.5 Hz.

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Generators in parallel : Example

The total power supplied by the generators equals the load power:

The system frequency can be found from:

The powers supplied by each generator are:

21 PPPload +=

MwffsPMwffsP

sysnlp

sysnlp

1)6061(*1)(

5,1)605,61(*1)(

221

111

=−=−=

=−=−=

Hzss

Pfsfsf

ffsffsPPP

pp

loadnlpnlpsys

sysnlpsysnlpload

6011

5,261*15,61*1

)()(

21

2211

221121

=+

−+=

+

−+=

−+−=+=

a) The power produced by a synchronous generator with a given slope and a no-

load frequency is)( sysnlp ffsP −=

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Generators in parallel : Example

Hzss

Pfsfsf

pp

loadnlpnlpsys 75,59

115,35,61*15,61*1

21

2211 =+

−+=

+

−+=

b) For the new load of 3.5 MW, the system frequency is

The powers supplied by each generator will be:

c) If the no-load frequency of G2 increases, the system frequency is

And the powers will be:

Hzss

Pfsfsf

pp

loadnlpnlpsys 5,59

115,361*15,61*1

21

2211 =+

−+=

+

−+=

MwffsPMwffsP

sysnlp

sysnlp

5,1)5,5961(*1)(

2)5,595,61(*1)(

222

111

=−=−=

=−=−=

MwffsPP sysnlp 75,1)75,595,61(*1)( 1121 =−=−==

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Power Flow Control (PFC)

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The integration of different power sources requires a power flow control. The reasons for this are:

• In a meshed power system, low impedance lines may be subject to overload, while parallel paths are underutilized. Power flow control must regulate this situation

• Energy sellers need power flow control in order to properly supply the loads of their distribution lines.

• In distributed generation grids (DGG), it may happen that there is a low voltage at heavily loaded lines or a high voltage at lightly loaded lines. These are undesirable occurrences and power flow control must generate the corrective actions to solve such problems. The corrective actions are related with power factor regulation by means of SVC (supply of reactive power to certain points)

• Transient and dynamic stability control issues require also power flow control.

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Regulation of P and Q between a source and a load

Equivalent circuit of one phase

δϕ sincos 11 ⋅=⋅ EIXT

Voltages vector diagram (RT is negligeable)

From vector diagram it can be derived that

Power diagram

i.e.

multiplying by 3U we get the power of the three phase system

similarly

δϕ sincos 11 ⋅=⋅

TXEI

δϕ sin3cos3 11 ⋅

⋅=⋅=

TXEUUIP

δδϕ sin)cos(3sin3 11 ⋅−⋅=⋅= UEXUUIQ

T

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Regulation of P and Q between a source and a load

δsin.XVVP LS

L = jXIVV SL −=

The regulation of δ angle allows the control of active and reactive power flow (PSR, QSR) between a source (VS) and a load (VR).

jX ISourceLoad

−= δcos

R

SRSL V

VXVVQ

LV

LP

LQ

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Two machines power flow in case of | Vs| =| Vr|

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If Vs and Vr are imposed by the machines to be equal, the P and Q curves as a function of δ will be as shownMaximum power will be transferred when δ=90º

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16 kWp Generació FV

26 kWh Bateries d’acumulació 4 Carregadors VE

Xarxa elèctricaSistema de control

Sistema de monitorització

CDP

Example CIRCUTOR AUTOCONSUMO

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CDP

BMSBattery Management

System

Control Dinámico de Potencia

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3 x 3,5 kWSingle phaseinverters

Power DynamicControl CDP-0

6,3 kWpPV arrayDC String,

AC GenerationPower StudioScada

efm-pvcar.circutorenergy.com

Example

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Monitorización con Power Studio SCADA

Renewable energy EV’s Charging system management

PV POWER

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Estabilización de la tensiónen cargas alejadas de BT

SVCJosep BalcellsUPC- Grup TiegMayo de 2014

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El problema clásico de distancia y carga variable

0MW Efecto Ferranti

800 kmLongitud de línea

400kVCarga Natural Objetivo 800 MW

1000MW Colapso del Sistema

Línea de transmisión de 400 kV(no compensada)

400kV400kV

800 MWGeneración

800 MWCarga

400kV

Potencia

400kV

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El problema moderno de generación y carga variable en micro-redes

Utility GridWind farm

CombinedGeneration Photovoltaic

Micro-Turbine

ResidentialCustomers

IndustrialLoad

Battery Storage

CommercialCustomer

CentralPower Plant

~ _

~ ~CB

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FACTS : Flex ible AC Transmission SystemS

Los sistemas FACTS son sistemas basados enfiltros LC y electrónica de potencia con elobjetivo de mejorar el control de flujo depotencias (P y Q) y la regulación en lineas dedistribución.Suele aplicarse a MT, pero con las microredesempieza a ser interesante en BT

Los sistemas FACTS más comunes son:• Static VAR Compensator - SVC• Thyristor Controlled Series Compensator -TCSC• Thyristor Controlled Phase Angle Regulator TCPAR• Static Synchronous Compensator - StatCom• Solid State Series Compensator - SSSC• Unified Power Flow Controller - UPFC

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Compensadores de var: Analogía mecánica

Solución: Apoyos intermedios== Inyección de Energía Reactiva, SVC

T1068

Mecánica: Caída del cable en puntos alejados de los apoyosEléctrica: Caida de V en puntos alejados de la fuente

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Estructura de un compensador SVC

TCR Filtro Filtro HPFiltro

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Diagrama Vectorial de un compensador SVC

Fuente Cargas

IL

X R

VF VL

IS =IL + Iq

Iq

SVC

Ireact IS=IL

Iact R.IS

X.ISVL < VF

b) Sin compensación de reactiva VL<VF

VF

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IreactIq

Iact=IS

VF

X.IS

VL < VF

c) Compensación de reactiva a cos ϕ =1 VL<VF

R.ISIL

Diagrama Vectorial de un compensador SVC

Fuente Cargas

IL

X R

VF VL

IS =IL + Iq

Iq

SVC

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d) Control de tensión VL con consigna VL=VF (Requiere sobrecompensación)

Ireact

Iact

VFIq

VL = VF

R.IS

X.ISIS

IL

Diagrama Vectorial de un compensador SVC

Fuente Cargas

IL

X R

VF VL

IS =IL + Iq

Iq

SVC

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Diagrama Vectorial de un compensador SVC

Fuente Cargas

IL

X R

VF VL

IS =IL + Iq

Iq

SVC

e) Control de tensión VL con consigna VL>VF (Requiere fuerte sobrecompensación)

Ireact

Iact

VF

Iq

VL > VF R.IS

X.ISIS

IL

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Flujo de Potencias en una línea de distribución

jX.IS

ILq

ILd

Vsmin=VF

IqVL

IS=IL+Iq

IL

ϕ

θ

θ

Obsérvese que VL puede ser mayor que VF dependiendo de lo grande que sea Iq

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∆I

∆V

V

I

VrefXCC

VLVF

∆V

∆I

Carga

IVX CC ∆

∆≈

Obtención de la impedancia de red

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Necesidades de potencia inductiva QL

qLFFL IU3Q =

jX.IS

ILq

ILd

Vsmax=VF

IqL

VL

IS=IL+IqL

ILϕ

θθδ

S

LqqL

SL

2maxF

2S

2L

III

XIV2V)XI(Vsen

−−=

−+=θ Datos: UFF, VFmax, X, ILd, ILq

Para cada IqL o QL permite

calcular VL

Aplicando el teorema de los senos se deduce que

36T1068

Necesidades de potencia capacitiva QC

jX.IS

ILq

ILd

Vsmin=VF

IqC

VL

IS=IL+IqC

IL

ϕ

θ

θδ

qCFFC IU3Q =

Datos:UFF, VFmax, X, ILd, ILq

Para cada IqL o QLpermite calcular VL

S

LqqC

SL

2minF

2S

2L

III

XIV2V)XI(Vsen

−=

−+=θ

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Diagrama de control de un compensador SVC

SVC. Tensión VL en función de Qc

380

385

390

395

400

405

-100 -50 0 50 100 150 200

Potencia reactiva inyectada (kvarC)

Tens

ión

en e

l PC

(V)

Disponemos de una hoja excel que calcula la curva

38T1068

TCR

Power Source

Controller NationalCompact Rio

Mains Reactance

Step 1 Step 2 Step 3

Load

HOSTTARGET

ETHERNET

SVC Maqueta de laboratorio 1kvarL+3kvarC

39T1068

• Controlador NI compact RIO 9074– FPGA Spartan III– uP PowerPC– 2 ports Ethernet– 1 port RS-232

• I/O– Entradas Analógicas (tensión) ±10 V

(NI 9215)– Entradas Analógicas (corriente) ±5 A

(NI 9227)• CPC 3i-4MRS

– Driver a paso por cero para TSC– Conexión a controlador RS-485

• CPC 3i-4LRS– Control de fase para TCR– Conexión a controlador RS-485

HOSTTARGET

ETHERNET

SVC Maqueta de laboratorio : Controlador

40T1068

SVC Maqueta de laboratorio 1kvarL+3kvarCCircuito de Potencia

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Ahora… en serio!!! Maqueta de 200kvar

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Ahora… en serio!!! Maqueta de 200kvar

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SVC-BT CIRCUTOR

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SVC-BT CIRCUTOR: Control

Obsérvese que en lugar de regular cos ϕregulamos tensión. En general esto supone sobrecompensar si VL deseada es > que VF

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TSC: Conexión

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TSC: Desconexión

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TCR Formas de onda de la corriente

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Medidas de campo en el TCR

CH1- Tensión en bornes del tiristor , CH2- Corriente de una de las ramas de reactancia (invertida), CH3 – Impulsos a tiristores (Ángulo de disparo aprox 90º)

CH1- Tensión en bornes del tiristor , CH2- Corriente de una de las ramas de reactancia (invertida), CH3 – Impulsos a tiristores (Ángulo de disparo aprox 95º)

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Medidas de campo en el TCR

CH1- Tensión en bornes del tiristor , CH2- Corriente de una de las ramas de reactancia (invertida), CH3 – Impulsos a tiristores (Ángulo de disparo aprox 90º)

CH1- Tensión en bornes del tiristor , CH2- Corriente de una de las ramas de reactancia (invertida), CH3 – Impulsos a tiristores (Ángulo de disparo aprox 170º)

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Medidas de campo en el TCR

CEBADO CON SINCRONISMO EQUIVOCADO

CH1- Tensión en bornes del tiristor , CH2- Corriente de una de las ramas de reactancia (invertida),

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380

385

390

395

400

405

410

1

123

245

367

489

611

733

855

977

1099

1221

1343

1465

1587

1709

1831

1953

2075

Second

Volta

ge Medida

Consigna

Regulación lenta: Refresco de consignas TSC: 10s , TCR: 1s

Medidas en campo:Valores de la tensión trifásica

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Medidas en campo:Valores de la tensión trifásica

Períodono regulado

Períodoregulado

Períodoregulado

Períodono regulado

Períodono regulado

Cambios de consigna

Tens

ión

trifá

sica

pro

med

io

Tiempo (s)

Regulación rápida: Refresco de consignas cada 3 ciclos

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Conclusiones SVC en baja

• El SVC permite regular la tensión a final de línea en redes blandas• Generalmente si Vfinal linea >= Vorigen requiere sobrecompensación• Con regulación rápida (Refresco de consignas cada 3 ciclos) el sistema permite una regulación excelente• Podemos pensar en la regulación fase a fase para sistemas con cargas desequilibradas• La regulación fase a fase llevará asociada una acción de equilibrado y un mejor reparto de potencias activas• El esfuerzo para sacar al mercado este producto es mínimo, pues se basa en un regulador COMPUTER Plus con ligeros cambios de software y la parte de potencia está formada por una batería estática + un TCR, que es muy similar• Ingenieria :

• Terminar algoritmos del COMPUTER Plus• Terminar rediseño de CPC3i para controlar inductancias• Probar con reactancias trifásicas un sistema equilibrado y con reactancias de 4 patas uno desequilibrado• Tiempo estimado a mercado 2 meses• Detectada necesidad en la división de renovables

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SVC en MT

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SVC en MT: Detalle de los tiristores

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Otros métodos de regulación: UPFC

• Permite controlar la tensión, la impedancia y el ángulo• Controla P y Q en la línea y por tanto el flujo de potencia

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Principio de Operación del UPFC

Convertidor Paralelo:Toma Q de la red y suministra QEn promedio no suministra P salvo pérdidas

SVRV '

RV

injV

jX

I

Convertidor Serie

ConvertidorParalelo

Convertidor Serie:Toma P y Q y uministra P y Q

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UPFC – Convertidores en MT o en BT

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En la integración de fuentes juega un papel esencial el

control de convertidores

Debemos distinguir entre regulación con generación y carga

próximas o cargas alejadas

El conjunto requiere sistemas de supervisión y control

Comunicaciones basadas en PLC

Conclusiones