1. introduction 2. e-on guidelines 3. modelling 4. controller design 5. simulation results 6....

1. Introduction

2. E-On Guidelines

3. Modelling

4. Controller Design

5. Simulation Results

6. Conclusion

Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power PlantsNORPIE / 2004 Nordic Workshop on Power and Industrial Electronics

14-16 June, 2004 Trondheim, Norway

FACULTY OF ELECTRICAL ENGINEERINGDEPARTMENT OF ELECTRICAL MACHINES AND DRIVES

Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants

Balduino Rabelo Wilfried Hofmann Andreas Basteck Martin Tilscher

NORPIE‘04 - Nordic Workshop on Power and Industrial Electronics14-16 June, 2004

Trondheim, Norway

VOITH TURBOCONTROLABLE DRIVES

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



1. Introduction2. E-On Guidelines3. Machine Modelling4. Controller Design5. Simulation Results6. Conclusion

Topics

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



In a project with the Voith Co. the AEM Co. and the TU Dresden preliminary studies of a windmill using a hydrodynamic torque converter (VORECON) were carried out.

The TU Chemnitz accomplished the following tasks:

•Modelling and simulation of a synchronous generator

•Emulation of the E-On cases for power plant connection to the electrical grid

•1. Synchronisation and connection with the mains supply•2. Reactive power exchange with the net•3. Load drop•4. Active power limiting with frequency variation•5. Short-circuit behaviour

Motivation

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Why?•Further expansion of wind energy. 2010 - 20,000 MW 2020 – 40,000 MW

•European interconnected system can bare a maximum drop of 3,000MW •Wind generators will have to support the grid in case of faults

Who?•Wind farms with more than 100 MW connected to the high voltage and extra-high voltage grids.

How?

2 - Reduce the active power and frequency fluctuation. 10% Pc/min1 - Support the grid in case of 15% to 60 % voltage drops for not more than 3s

3 - Limit the cut-in in 1.2 of the rated power Pc at the connection point4 - Control the reactive power in a desired range

Verification of compliance with the new norms

•Guideline from manufacturers and measuring institutes

Ergänzende Netzanschlussregein für Windenergieanlagen, 1.8.2003, E-on Netz Ltd.

Guidelines for net connection from E-On

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Active Power Limiting Curve

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Enlarged Range

Reactive Power Control Range

t < 30min

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Voltage Drop Profile

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Hydrodynamic Torque Converter VORECON

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Dynamical Model of the VORECON

Rotor Hub Gear Box Vorecon - Voith Coupling Brake

InterfaceTU Chemnitz

Torque

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



The voltage equation of a synchronous machinewhere the underline defines a complex vector

Description in a rotating reference frame

ssssdt

diRu

sdrsqsqssq

sqrsdsdssd

dt

diRu

dt

diRu

q

d

sqsds juuu sqsds juuu

su

squsdu

r

Basic Equations

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



sdsqsqsdpe iiZM 2

3The electromechanical torque expression

The dynamical interactions between the stator, damping and field circuits are given the following operators

1

1

0000

2

2

''

d

'

d

''

d

'

d

''

d

'

d

''

d

'

dsdLd TTsTTs

TTsTTsL)s(G

''

q

''

q

sqLq sT

sTL)s(G

01

1

'

d

'

d

f

'

sdsdf sT

T

L

LL)s(G

0

0

1

)s(u)s(G)s(i)s(G)s( ffsdLsd d

)s(i)s(G)s( sqLqsq

The fluxes can be obtained by the expressions

Torque and Flux Linkage Equations

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Block Diagram of the Synchronous Generator

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Control Variables

Wind Turbine

Vorecon Synchronous Generator

PitchAngle

Guide VanePositionH

Field Voltageuf

The system has 3 control variables:- pitch angle and the guide vane position control the main power flow - field voltage controls the magnetising of the synchronous generator and the reactive power flow.

This latter can also influence the stability of the system.

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Induced Voltage Controller

The induced voltage controller UPol uses the field voltage uf to regulate the flux

In high-powered generators these self-excited control schemes present a faster inner field current control not shown here

Considering the speed constant the induced voltage dynamics depends only on the flux

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



The field controller has to accomplish the following tasks:• regulate the induced voltage at the machine terminals during synchronisation• control the power factor or the reactive power flow during normal operation• guarantee the dynamical stability during undesired transient conditions

An outer power factor control loop influences the induced voltage in normal operating conditions, as well as compensates the voltage drop over the stator windings during loading

Controller Tasks and Structure

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Controller Optimisation

The induced voltage controller posses 2 basic PI structures for synchronisation and for normal operation that were optimised by module (BO) and by symmetrical optimum (SO) rules, respectively.

-100

-50

0

50

100

150

10-2

100

102

-180

-135

-90

-45

0Phase (deg)

BO openBO closedSO openSO closed

Bode Diagram

Frequency (Hz)

Mag (dB)

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Synchronisation Starting Currents

1.2 1.25 1.3 1.35 1.4 1.45-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Iabc

/In

t(s)

Connecting the machine to the mains with an angle error from less than 10 degrees gives transient currents which peak values lie under 40 % of rated value vanishing in less than one second, as shown in the left figure.

With a neglectiable angle error the start-up currents are much smaller, as can be observed in the right figure.

t(s)

stator phase currentsstator phase currents

t(s)

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Torque Step from No-load to Rated Value

5 5.5 6 6.5 7 7.5 8-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

x 104

t(s)

me (Nm)

ma (Nm)

5 5.5 6 6.5 7 7.5 8-3

-2

-1

0

1

2

3

Iabc

/In

t(s)

An extreme power step is simulated where the input torque is increased from no-load condition to rated torque.

The generator is kept in synchronism and the currents reach the rated value after the transient period.

t(s) t(s)

generator torque stator phase currents

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



26 27 28 29 30 31 32 33-2.1

-2

-1.9

-1.8

-1.7

-1.6

-1.5

-1.4

-1.3

-1.2x 10

4

t(s)

me (Nm)

ma (Nm)

Coupling with the Reactive Power Control

26 27 28 29 30 31 32 330.15

0.2

0.25

0.3

0.35

0.4

t(s)

Sinus Phi

Cos Phi 0.98 ind

Cos Phi 0.92 ind

After a negative mechanical torque step over-shoots on the electromechanical torque occur during the transient period. The well-damped power factor controller reduced the over-shoots due to the coupling with the active power canal and let the actual value reach the reference smoothly after some seconds.

t(s) t(s)

generator torque power factor

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Power Factor Control

The power factor controller presents good responses over the desired range. Higher damping is observed on the capacitive range, as expected.

0 50 100 150 200-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

t(s)

Sin

us P

hi

IstSoll

induktiv kapazitiv

cos

actualref

inductive capacitive

power factor

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Power Factor Step

33 33.5 34 34.5 35-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

t(s)

Sinus Phi

Cos Phi 0.92 kap

Cos Phi 0.92 ind

33 33.5 34 34.5 35-3

-2.8

-2.6

-2.4

-2.2

-2

-1.8

-1.6

-1.4

-1.2

-1

-0.8x 10

4

t(s)

me (Nm)

ma (Nm)

The power factor step presents a retarded response due to the coupling with the active power channel. The increase on the torque caused by the reference power factor step is less damped than the reaction caused again on the power factor. Such extremes reactive power steps must be avoided in the normal operation of the generator in order to avoid the observed torque steps.

t(s)t(s)

power factor generator torque

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 24-600

-400

-200

0

200

400

600

t(s)

Dre

ipha

sige

r N

etzs

pann

unge

n (V

)

19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 24-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8x 10

4

t(s)

Dre

hmom

ente

(N

m)

me

mAntriebe

19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 24-4

-3

-2

-1

0

1

2

3

4x 10

4

t(s)

Dre

ipha

sige

r S

tato

rstr

öme

(A)

The 3-phase voltage drop profile from E-ON have a similar effect of a 3-phase short-circuit on the machine.

After the well-known transient periods further oscillations appear on the torque and on the currents due to the slow increase of the mains voltage.

Voltage Drop

t(s)

t(s)t(s)

generator torque stator phase currents

net voltages

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



The oscillations observed previously on the torque and on the currents are also observed on the speed.

The power angle crosses the stability limit for a short period of time. The machine is kept in synchronism due to the reached dynamical stability enabled by the power factor controller.

However, the required field voltages to magnetise the machine in such cases are higher than the maximum allowed.

19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 241440

1460

1480

1500

1520

1540

1560

t(s)

Dre

hzah

l (rp

m)

19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 24

0

20

40

60

80

100

120

t(s)

Pol

radw

inke

l (°)

break down

Rated

Power Angle and Speed

t(s)t(s)

n r

pm)

pole pitch angle rotor speed

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



Load Drop

A 100 % load drop was simulated in order to verify the possible overvoltage effects on the machine terminals.

The induced voltage increases after at the load drop moment but the field controller actuates faster and limits the increase ratio letting the intern voltage in acceptable levels until switching off or reloading.

stator phase currents induced voltage

t(s) t(s)

1. Introduction

2. E-On Guidelines

3. Modelling



6. Conclusion



A synchronous machine classical model was used to simulate different situations before and after synchronisation with the electrical grid.

A voltage regulator for the field excitation of the synchronous generator was designed. This controller has to guarantee stable operation of the generator under various conditions including faults.

Simulation results show the good performance of the controller. With the already existing controller the machine is kept stable during extreme conditions like torque steps and reactive power variations. Faulty conditions were also simulated.

Further studies will investigate the effects of faulty conditions on the mechanical drive train caused by high electromechanical torque and its harmonics and of the distribution line and the transformer on the performance of the machine under voltage drops.

Summary and Future Works

1. introduction 2. e-on guidelines 3. modelling 4. controller design 5. simulation results 6....

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