Implications of the DC Voltage Control Strategy on the Dynamic - - PowerPoint PPT Presentation

SLIDE 1

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 1

Implications of the DC Voltage Control Strategy on the Dynamic Behavior of Multi-terminal HVDC following a Converter Outage

• F. Gonzalez-Longatt1,2, J. Roldan3
• M. Burgos-Payán3, V. Terzija4

1 Coventry University

2 Venezuelan Wind Energy Association 3 Universidad de Sevilla 4 The University of Manchester

SLIDE 2

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 2

• I. Outline
• I. Introduction
• II. Control Strategies for MTDC Networks Operation

(i) Inner-Fast Current Controller, (ii) DC Voltage Controller, (iii) AC Voltage Controller, (iv) Active Power Controller, (v) Reactive Power Controller.

• III. DC Voltage Control: Methods

(i) Direct Voltage-Droop Method (ii) Voltage-Margin Method

• IV. Simulations and Results

(i) Case I: Sudden load increase, (ii) Case II: One Converter Outage

• V. Conclusions

SLIDE 3

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 3

• I. Introduction (1/2)
• The EU and the G8 Heads of

Government committed their countries in 2009 to an 80 % reduction in Green House Gas emissions by 2050.

• International consensus to reach this

target requires the EU to achieve a 'nearly zero-carbon power supply‘.

• Supergrid is the name of this future

electricity system that will enable Europe to undertake a once-off transition to sustainability.

• Multi-terminal

HVDC (MTDC) using Voltage Source Converter (VSC) is the most appropriate technology to enable the concept of Supergrid.

SLIDE 4

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 4

• I. Introduction (2/2)
• The power injections (Pi) in a DC grid

are controlled by the converters.

• On a MTDC grid as Supergrid, the

power flow into, or out of, each converter can be dynamically changed without any reconfiguration of the HVDC grid.

• Although Supergrid should allow the

full control of active power on all converters, several control challenges arise from this condition.

• The purpose of this paper is to

analyze the potential implications of the DC Voltage Control Strategy on the dynamic behavior of Multi- terminal HVDC following a Converter Outage.

Scotland Shore Line (5GW) England Shore Line (24GW)

NorNed2 NorNed

(7GQ Interface Capacity)

Denmark Shore Line (3.5GW)

SLIDE 5

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 5

• II. Control Strategies for MTDC (1/3)

Schematic representation of MTDC control system hierarchy

The master control optimizes the overall performance of the MTDC by regulating the DC side voltage. It is provided with the minimum set of functions necessary for coordinated operation of the terminals in the DC circuit, i.e. start and stop, minimization of losses, oscillation damping and power flow reversal, black start, AC frequency and AC voltage support.

The terminal controllers determine the behavior of the converter at the system bus. They are designed for the main functions for controlling: active power (P), reactive power (Q), AC and the DC voltage (Vac, Udc)

Time Scale

VSC

dc

n i

P

, dc i

P

, dc i

U

i

V

, g i

P

, l i

P

1 g

P

1 l

P

SLIDE 6

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 6

• II. Control Strategies for MTDC (2/3)

Terminal Controllers are based on locals actions and measurements. Wide-area measurement and control can improve the system performance.

ref

Q Q

ac

V

, ac ref

V

* q

i

* d

i

ref

P P

dc

U

, dc ref

U

, ac Ctrl

V

Ctrl

Q

, dc Ctrl

U

Ctrl

P

Terminal Controller

SLIDE 7

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 7

• II. Control Strategies for MTDC (3/3)

ref

Q Q

ac

V

, ac ref

V

* q

i

* d

i

ref

P P

dc

U

, dc ref

U

, ac Ctrl

V

Ctrl

Q

, dc Ctrl

U

Ctrl

P

 

ref

Q Q

, , i Q p Q

K K s 

* q

i

max

i 

max

i   

, , i Udc p Udc

K K s 

* d

i

max

i 

max

i 

, dc ref

U

dc

U  

ac

V

, ac ref

V

, , i Vac p Vac

K K s 

* q

i

max

i 

max

i   

ref

P P

, , i P p P

K K s 

* d

i

max

i 

max

i 

        

* d

v

* q

v

, d ref

i

, q ref

i

d

i

q

i

d

v

q

v

, , i id p id

K K s 

, , i iq p iq

K K s  L  L 

Q Controller P Controller Udc Controller Vac Controller Idq Controller

Terminal Controller

SLIDE 8

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 8

III. DC VOLTAGE CONTROL

When the active power is to be transmitted from Terminal B to Terminal A (PA<0, PB>0), the voltage margin (Udc) is subtracted from the DC reference voltage for Terminal A.

(i) Voltage Margin Method (VMM) (ii) Voltage-Droop Method (VDM)

When Udc drops the slack converter station (VSCA) will increase the active power injection in the DC grid PA until a new equilibrium point.

,A dc

U

A

P

dc

U 

upper

P

lower

P

,A dc

U

A

P

Slope mc

dc

U 

Initial operating point Inverter Lower limit Rectifier “a” Upper limit

upper

P

lower

P

, a dc ref

U

“b”

b ref

P

b ref

U

a ref

P

SLIDE 9

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 9

• IV. Simulations and Results (1/2)
• The dynamic behavior of AC/DC Test System is analyzed based
• n time-domain simulations. DigSILENT

PowerFactoryTM v14.0.525.1.

• Case I: The effect of sudden load increases on power flows and

transient response in the AC/DC Test System.

• Case II: The effects of a converter outage on the dynamic response

are also analyzed.

AC Test System: of Stagg and El-Abiad. DC Test System: VSC MTDC system.

SLIDE 10

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 10

• IV. Simulations and Results (2/2)
• An sequential solution algorithm is used for the AC/DC

power flow solution.

• That solution is used as initial conditions for the dynamic

simluations.

fglongatt

PowerFactory 14.0.525 Stagg and El-Abiad Test System DC Voltage Control on Multi-Terminal HVDC Juan Manuel Roldan Francisco M. Gonzalez-Longatt, PhD Project: fglongatt Graphic: AC Power Networ Date: 01/01/2012 Annex:

Elm South North Lake Main

Bus 5

98.94 0.99

• 4.20

Bus 4

99.20 0.99

• 4.31

Bus 3

99.50 1.00

• 3.94

Bus 2

100.00 1.00

• 2.44

Bus 1

106.00 1.06 0.00

20/10

20.00 10.00

G ~

G2

40.00

• 106.69

113.94

External Grid

135.98.. 85.82 .. 0.85

2-5

25.62

• 0.83

25.64

2-5

• 25.36
• 1.35

25.64

45

• 0.36
• 1.26

3.70

45

0.36

• 3.65

3.70

2-4

• 17.43
• 0.26

17.88

2-4

17.62

• 3.15

17.88

3-4

22.26 1.66 22.64

3-4

• 22.21
• 3.48

22.64

2-3

13.90

• 3.69

14.37

2-3

• 13.78

0.06 14.37

1-3

36.08 14.89 38.87

1-3

• 34.93
• 16.73

38.87

1-2

99.90 70.93 119.03

1-2

• 97.14
• 69.02

119.03

60/40

60.00 10.00

40/5

40.00 5.00

45/15

45.00 15.00

DIgSILENT

fglongatt

PowerFactory 14.0.525 VSC Multi-Terminal HVDC System DC Voltage Control Dynamic Case Francisco M. Gonzalez-Longatt, PhD Project: Graphic: DC Power Netwo Date: 01/01/2012 Annex:

RECTIFIER INVERTER INVERTER Multi-Terminal HVDC System

Bus 5

98.94 0.99

• 4.20

Bus 3

99.50 1.00

• 3.94

Bus 2

100.00 1.00

• 2.44

Bus 8

148.24 0.99 0.00

Bus 7

149.70 1.00 0.00

Bus 6

154.22 1.03 0.00 35.00 5.00 18.55 0.00

• 60.00

40.00

VSC 37

18.55 0.00

VSC 37

• 19.62

0.00

VSC 58

35.00 5.00

VSC 58

• 36.23

0.00

VSC 26

• 60.00

40.00

VSC 26

57.90 0.00

6-7

• 28.94

0.00 29.00

6-7

29.82 0.00 29.00

6-8

28.09 0.00 27.32

6-8

• 27.00

0.00 27.32

7-8

• 9.24

0.00 4.67

7-8

9.33 0.00 4.67

DIgSILENT

SLIDE 11

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 11

Models on DSL

FRAME P-Q Controller: Active and Reactive Power Controller (P-Q Mode)

Frame: P-Q Mode Developed by: Juan M. Roldan Francisco M. Gonzalez-Longatt, PhD 01/01/2012 fglongatt@ieee.org

P controller ElmDsl*

Pref 1 2

Current Controller ElmDsl*

1 2 3 1

PLL measure ElmPhi*

1 2

P-Q meas StaPqmea*

1

VSC ElmVscmono*

1 2 3 1

Control f ElmDsl*

fref 1

Q controller ElmDsl*

Qref 1

FRAME P-Q Controller: Active and Reactive Power Controller (P-Q Mode)

iq(1) iqref idref DPf id(1) Q Fmeas P sinref cosref Pmq Pmd

DIgSILENT

FRAME Control Udc-Q: Controller Udc-Q FRAME Udc-Q Mode Developed by: Juan M. Roldan Francisco M. Gonzalez-Longatt, PhD 01/01/2012 fglongatt@ieee.org VSC-1 ElmVscmono*

1 2 3 1

Vdc Control ElmVdc*

Vdc_ref 1 2 3

Current C.. ElmDsl*

1 2 3 1

Idc meas StaImea* Vdc meas StaVmea* P-Q meas StaPqmea* Q control ElmDsl*

Qref 1

Vac meas StaVmea*

1

transformation phase .. ElmDsl*

iq 1 2 3 1

PLL ElmPhi*

1

FRAME Control Udc-Q: Controller Udc-Q ud iq id idref iqref Pmq Pmd Idc Vdc Q ui ur cosref sinref

DIgSILENT

idq controller: Current Controller, Internal-Fast Loop

Developed by: Juan M. Roldan and F. Gonzalez-Longatt, PhD Project: Multi-Terminal HVDC Date: 01/01/2012 fglongatt@ieee.org

• Pmdq limiter

Max

1 1

• Current Limit..

Max_I

1 1

{K (1+1/sT)} K,T Max_Pm Min_Pm {K (1+1/sT)} K,T Max_Pm Min_Pm

idq controller: Current Controller, Internal-Fast Loop

1 2 3 1

Pmq Pmd iql idl iqref idref uq ud diq did iq id

DIgSILENT

SLIDE 12

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 12

DC Voltage Controllers: DSL Models

Udc-P droop controller: Udc Droop Controller

Droop Udc-P Droop Controller Developed by: Juan M. Roldan Francisco M. Gonzalez-Longatt, PhD Project: Multi-Terminal HVDC 01/01/2012, fglongatt@ieee.org

• {K (1+1/sT)}

Kp,Tp Max_I Min_I K Kv Limiter with input si..

• Udc-P droop controller: Udc Droop Controller

2 1 4 3 5

I_min I_max Idref u Pref P dP Plower KDV DV Pmax Udc Udcref

DIgSILENT

Udc Controller: Voltage-Margin Method (VMM)

Udc-P Voltage-Margin Method Developed by: Juan M. Roldan Francisco M. Gonzalez-Longatt, PhD Project: Multi-Terminal HVDC 01/01/2012, fglongatt@ieee.org

Constant1/mc {K (1+1/sT)} Ku,Tu Max_I Min_I Limiter with input signals

• Udc Controller: Voltage-Margin Method (VMM)

2 1 5 3 4

I_max I_min

• 11

u1 Ud Idc

• 1

du Pupper Plower Idref U Udc_ref Udc

• 12

DIgSILENT

 

, , i Udc p Udc

K K s 

d

i

max

i 

max

i 

, dc ref

U

dc

U 1

c

m  

ref

P P

SLIDE 13

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 13

Case I: Sudden Load Increase (1/2)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 29 30 31 32 Time (s) Power 6-7 (MW) Margin Droop A Droop B 0.1 0.2 0.3 0.4 0.5 0.6 0.7 27.5 28 28.5 29 Time (s) Power 6-8 (MW) Margin Droop A Droop B 0.1 0.2 0.3 0.4 0.5 0.6 0.7 6 7 8 9 10 11 Time (s) Power 7-8 (MW) Margin Droop A Droop B

RECTIFIER INVERTER INVERTER Multi-Terminal HVDC System

Bus 5

98.94 0.99

• 4.20

Bus 3

99.50 1.00

• 3.94

Bus 2

100.00 1.00

• 2.44

Bus 8

148.24 0.99 0.00

Bus 7

149.70 1.00 0.00

Bus 6

154.22 1.03 0.00 35.00 5.00 18.55 0.00

• 60.00

40.00

VSC 37

18.55 0.00

VSC 37

• 19.62

0.00

VSC 58

35.00 5.00

VSC 58

• 36.23

0.00

VSC 26

• 60.00

40.00

VSC 26

57.90 0.00

6-7

• 28.94

0.00 29.00

6-7

29.82 0.00 29.00

6-8

28.09 0.00 27.32

6-8

• 27.00

0.00 27.32

7-8

• 9.24

0.00 4.67

7-8

9.33 0.00 4.67

Sudden Load Increase

Voltage margin method produces the smallest stress on AC system. Voltage-Droop method increases power transfer during initial response.

40 P MW  

SLIDE 14

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 14

Case I: Sudden Load Increase (2/2)

• The blue line shows the bus voltage’s

response with only one voltage controller operating, voltage margin method.

• The red line represents the dynamic

response when a voltage droop controller (mc = -0.1) is operating on converter station VSC26.

• The

transient

• ver-voltages

and under-voltages are reduced as expected using the droop control.

• The slopes of the voltage-droop

controller considered in this simulation are 1/mc= -10.0, -8.0, -2.0 p.u. for converters VSC26, VSC37, VSC58 respectively.

0.2 0.4 0.6 0.8 1 1 1.01 1.02 1.03 1.04 Time (s) Bus Voltage (p.u) 0.1 0.15 0.2 1.01 1.02 1.03 Margin Drop 0.2 0.4 0.6 0.8 1 0.97 0.975 0.98 0.985 0.99 Time (s) Bus Voltage (p.u) 0.05 0.1 0.15 0.97 0.975 0.98 0.985 0.99 Margin Droop

Bus 5, AC voltage transient with margin and droop control strategies Bus 6, DC voltage transient with margin and droop control strategies

SLIDE 15

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 15

Case II: Converter Outage (1/2)

RECTIFIER INVERTER INVERTER Multi-Terminal HVDC System

Bus 5

98.94 0.99

• 4.20

Bus 3

99.50 1.00

• 3.94

Bus 2

100.00 1.00

• 2.44

Bus 8

148.24 0.99 0.00

Bus 7

149.70 1.00 0.00

Bus 6

154.22 1.03 0.00 35.00 5.00 18.55 0.00

• 60.00

40.00

VSC 37

18.55 0.00

VSC 37

• 19.62

0.00

VSC 58

35.00 5.00

VSC 58

• 36.23

0.00

VSC 26

• 60.00

40.00

VSC 26

57.90 0.00

6-7

• 28.94

0.00 29.00

6-7

29.82 0.00 29.00

6-8

28.09 0.00 27.32

6-8

• 27.00

0.00 27.32

7-8

• 9.24

0.00 4.67

7-8

9.33 0.00 4.67

Outage

X

36.23 P MW  

0.1 0.2 0.3 0.4 0.5 0.6 0.7 25 30 35 40 45 Time (s) Power 6-7 (MW) Margin Droop A Droop B 0.1 0.2 0.3 0.4 0.5 0.6 0.7

• 20
• 10

10 Time (s) Power 7-8 (MW) Margin Droop A Droop B 0.1 0.2 0.3 0.4 0.5 0.6 0.7 10 15 20 25 30 Time (s) Power 6-8 (MW) Margin Droop A Droop B

Reverse power Flow

Converter outage can create reverse power flows, overload on undersea cables and converter stations is a real possibility. Voltage-Droop method performs better.

SLIDE 16

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 16

Case II: Converter Outage (2/2)

• This simulation results are used to

investigate the effect of a distributed voltage droop control on bus 2 (VSC26).

• The response of bus voltage at bus 6

considering a perturbation based on the outage of VSC58 demonstrates how an incorrect selection slope value may causes transient responses with greater over-voltages on the DC bus (Droop B, green line).

• If voltage-droop slope is correctly

selected it can assist the main the voltage at slack bus 3 and the system can handling transients caused by

• ne converter station outage

0.2 0.4 0.6 0.8 1 1 1.05 1.1 1.15 1.2 Time (s) Bus Voltage (p.u) Margin Droop A Droop B 0.2 0.4 0.6 0.8 1 0.97 0.975 0.98 0.985 0.99 0.995 1 Time (s) Bus Voltage (p.u) 0.05 0.1 0.15 0.97 0.975 0.98 0.985 0.99 0.995 Margin Droop A Drrop B Bus 5, AC voltage transient with margin and droop control strategies Bus 6, DC voltage transient with margin and droop control strategies

SLIDE 17

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 17

Conclusions

• This paper presents simulation results show the effect of

DC Voltage control strategy on the dynamic behavior of bust voltages at multi-terminal HVDC following a converter-station outage: (i) voltage margin method and (ii) voltage-droop method.

• When two converters on the MTDC operate with DC

voltage droop characteristic, it appears a "collaborative scheme" for the DC voltage support, sharing the task of controlling the DC voltage.

• Simulation results demonstrate the voltage margin

control is capable to survive a converter outage just if this converter is operating on constant power mode.

SLIDE 18

CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 18

Any questions?

Francisco M. Gonzalez-Longatt, PhD, SMIEE, MIET Coventry University, Coventry, UK Website: www.fglongatt.org.ve Email: fglongatt@ieee.org