9/19/18

1

Enrique Acha

IEEE Sección Morelos

Cuernavaca, Morelos, México

September 18-20, 2018

9/19/18

AC or DC?

§ Thomas A. Edison or Nikola Tesla?

9/19/18

§ HVAC systems reconfigurations§ LVDC systems reconfiguration§ AC and DC µgrids§ Smart Grids

Content

9/19/18

HVAC Systems Reconfigurations

9/19/18

600 kV DC

Local generation and compensation

2200 MW

330 kV

Hydro-generation

431 km

220 kV

330 kV

8×270 MW thyristor bridges

8×270 MW thyristor bridges3600 A

(b)

210 kmLocal generation and compensation

800 MW

98 km

123 km

Hydro-generation

330 kV

330 kV220 kV

2 × 350 mm2

ACSR conductors

(a)

ABCD

Conventional AC transmission system layout in Fig. 10.13(a) in page 272 of J. Arrillaga – HVDC Transmission, IEE monograph

Converted AC transmission system to an AC and DC transmission system in Fig. 10.13(c) in page 272 of J. Arrillaga – HVDC Transmission, IEE monograph, IET, 1983 and 1988.

Original solution put forward in K.M. Jones and M.W. Kennedy, “Existing AC transmission facilities converted for use with dc”, IEE Conf. Publ. 107 on “High Voltage DC and/or AC power transmission”, London, 1973, pp. 253-260

9/19/18

(c)

330 kV220 kV

210 km 98 km 123 km

600 kV DC

4×180 MW VSCs

4×180 MW VSCs

2400 A

Local generation and compensation

2800 MW

Hydro-generation

431 km

600 kV DC

8×270 MW thyristor bridges

8×270 MW thyristor bridges2400 A

Reconverted AC transmission system to an all-DC transmission system using three bipoles, two bipoles using classical HVDC transmission (thyristor bridges and phase control) and one bipole using modern HVDC transmission (IGBT bridges and PWM control), with the option to tap on intermediate load and generation

9/19/18

LVAC Systems Reconfigurations

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Possibilities of Low-Voltage DC Distribution Systems in Finland

20 kV

20/1 kV 1/0.4 kV

1/0.4 kV

1/0.4 kV

20 kV

20/0.4 kV

20/0.4 kV

20/0.4 kV

20 kV

20/1 kV

1.5 kV DC DC/AC inverter at every customer

T. Kaipia, P. Salonen, J. Lassila, J. Partanen, ”Application of Low Voltage DC-Distribution System – A Techno-Economical Study”, 19th International Conference on Electricity Distribution (CIRED), Vienna, 21-24 May 2007. Low Voltage Directive (LVD 72/73/EEC) covering 75 to 1500 V DC.

9/19/18

Possibilities of Low-Voltage DC Distribution Systems in Finland

§ The components used in DC-distribution systems would be almost the sameas in AC-distribution systems except for the power electronic inverters

§ In Finland, current standards allow low-voltage underground cables to beused in DC systems if system voltage between two conductors is not higherthan 1.5 kV and between earth and conductor is not higher than 0.9 kV.

§ Assuming that AC cables can be used with no change inDC-distribution applications then the four conductors ofthe three-phase system may be arranged in variousways to transport power in DC form

Possible connection solutions for the unipolar configuration

L L

LN

V(a)

L L L

N

V(b)

L

N

V(c)

L

V

L

(d)

L

V

-V

L

N

Bipolar configuration

(e)

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Possibilities of Low-Voltage DC Distribution Systems in Finland

+

VDC

-

IDC

-IDC

Unipolar DC system

+

VDC

-

IDC

-IDC

+

VDC

-Bipolar DC system

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AC and DC µGrids

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According to the CIGRÉ C6.22 Working Group, Microgrid Evolution Roadmap: “microgrids are electricity distribution systems containing loads and distributed energy resources, (such as distributed generators, storage devices, or controllable loads) that can be operated in a controlled, coordinated way either while connected to the main power network or while islanded”

9/19/18

500 kW

33 kV

11 kV

1

Source: Freris and Infield –Renewable Energy

2302 kW and 689 kVAr

2

3

45

6

7

8

10

11

12

16

14

13

15

17400 V

PCC

1297m

304m

626m

391m

738m

492m

583m

1000m

1110m

539m

1154m

652m791m

583m

539m1253m

OH2

AC µGRID IN ISLANDED MODE

AC µGrids with DC DERs and Feeding into AC Loads

9/19/18

33 kV

11 kV

1

500 kW

Total load is2302 kW

2

3

45

6

7

8

10

11

1216

14

13

15

17400 V

1297m

304m

626m

391m

738m

492m 583m

1000m

1110m

539m

1154m652m

791m

583m

539m

1253m

DC µGrids Feeding into DC Loads

DC µGRID IN ISLANDED MODE

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Modelos

9/19/18

1 1 DCj

aV k m e Eϕ=

+

EDC

-

CDC

φma

1VI’’2 I’2

I2

jBeq

VALVE SET

CDC

jX1V0

G0

R1

+

EDC

-

11 : ak m ϕ∠1V 1I vRV

vRI

00 =I

21

*11

*'1

*1120

*1120

j)(

)Re(

VBIVIIVIV

IVIV

eq+=−=

=

sw

2

act2

nom2

0 GIIG ⇒⎟⎟

⎠

⎞⎜⎜⎝

⎛⋅

( )( )

1 11

2 21 10 01 sw 1

cos jsin

cos jsin ( j )0

vR vRa

a a eq

Y k m YI VVk m Y G k m Y BI

ϕ ϕ

ϕ ϕ

⎛ ⎞⎛ ⎞ − + ⎛ ⎞⎜ ⎟=⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟− − + += ⎝ ⎠⎝ ⎠ ⎝ ⎠

Voltage Source Converter (VSC) Model

§ A flexible and comprehensive model of a STATCOM is given below,

9/19/18

VSC Model with DC Cable Extension

V0R V0IGDC

I0R I0I

(c)

(a)

+EDC

-ma

V0IV0RGDC

vIV

I’’2 I’2

I2

jBeqCDC

jX1V0I

Gsw

R1

+

EDC

-

11: ak m ϕ∠1V 1I vIV

vII

(b)

9/19/18

0

0

R DC DC DCR

I DC DC DCI

I G G EI G G E

−⎛ ⎞ ⎛ ⎞⎛ ⎞=⎜ ⎟ ⎜ ⎟⎜ ⎟−⎝ ⎠ ⎝ ⎠⎝ ⎠

The nodal admittance matrix of the combined inverter VSC-cable system is:

where the nodal admittance of the cable is:

Adding the nodal admittance matrix of the rectifier VSC to the nodal expression of the VSC-cable system:

Point-to-Point VSC-HVDC Model

0

2 20 1 11 1

1 11

0

( j )

0

R DC DC DCR

I I IDC aI eqI swI DC aI I DCI

vI I I vIaI I

I G G EI G k m Y B G G k m Y E

I k m Y Y V

ϕ

ϕ

⎛ ⎞ −⎛ ⎞⎛ ⎞⎜ ⎟ ⎜ ⎟⎜ ⎟

= − + + + − ∠−⎜ ⎟ ⎜ ⎟⎜ ⎟⎜ ⎟ ⎜ ⎟⎜ ⎟⎜ ⎟ − ∠ ⎝ ⎠⎝ ⎠⎝ ⎠

1 11

2 21 10 1 1

2 21 10 1 1

1 11

0 0

( j ) 0

0 ( j )

0 0

R RvR aR R vR

R RR aR R aR eqR swR DC DC DCR

I II DCIDC aI eqI swI DC aI I

vII IvI aI I

Y k m YI Vk m Y k m Y B G G GI E

EG k m Y B G G k m YIVk m Y YI

ϕ

ϕ

ϕ

ϕ

⎛ ⎞⎛ ⎞ − ∠− ⎛ ⎞⎜ ⎟⎜ ⎟ ⎜ ⎟− ∠ + + + −⎜ ⎟⎜ ⎟ ⎜ ⎟= ⎜ ⎟⎜ ⎟ ⎜ ⎟− + + + − ∠−⎜ ⎟⎜ ⎟ ⎜ ⎟

⎜ ⎟⎜ ⎟⎜ ⎟ − ∠ ⎝ ⎠⎝ ⎠ ⎝ ⎠

These expressions may be expressed in terms of powers

9/19/18

VSC-HVDC System Models

DC Grid

DS

MG1

MG2

GDC2

GDC1

GDC3

VSC1

VSC2

VSC3

GDC

EDCR EDCI

PDCRvRV vIV

aRm aIm

Rectifier Inverter

[ ]

[ ]

[ ]

[ ] [ ] [ ] [ ]

1 1 1

1 1 1

Im Im

n n n

m

⎡ ⎤ ⎡ ⎤ ⎡ ⎤⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥ ⎢ ⎥

= −⎢ ⎥ ⎢ ⎥ ⎢⎢ ⎥ ⎢ ⎥ ⎢⎢ ⎥ ⎢ ⎥ ⎢⎢ ⎥ ⎢ ⎥ ⎢⎢ ⎥ ⎢ ⎥ ⎢⎣ ⎦ ⎣ ⎦ ⎣ ⎦

VSC,R RR VSC,R

RDC

VSC,R RR VSC,R

VSC,I II VSC,I

IDC

VSC, I VSC,

DC DCR DCI DC DC

F J 0 0 0 ΔΦJ

F 0 J 0 0 ΔΦF 0 0 J 0 ΔΦ

JF 0 0 0 J ΔΦF J J J ΔE

L LM M O M M O M M

L LL L

M M O M M O M ML L

⎥⎥⎥⎥⎥

( ) ( )( )

( ) ( )

r rr

r r

Δ⎡ ⎤ ⎡ ⎤⎡ ⎤⎢ ⎥ ⎢ ⎥Δ⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥⎢ ⎥ ⎢ ⎥=−

Δ⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥⎢ ⎥ ⎢ ⎥⎣ ⎦ Δ⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦

Δ

AC AC

VSC,R VSC,R

AC/DCVSC,I VSC,I

DC DC

AC/DC AC/DC

F ΨF Φ

JF Φ

F E

F Ψ

M M

M M

14 2 43 1 4 2 43

9/19/18

Multi-Terminal VSC-HVDC Model

DC ringDS1

DS2

DS3

AC2

AC1

AC3

9/19/18

Multi-Terminal VSC-HVDC Model

DC ring

DS1

DS2 DS3

AC2

AC1

AC3

DC DC

DC DC

DC

DC

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Multi-Terminal VSC-HVDC Model

DC ring

DS1

DS2 DS3

AC1

DC DC

DC DC

DC

DC

DC

DC

ctrlstorage

DCDC

ctrlstorage

9/19/18

AC/DC Micro-Grids

Micro-grid 1

v4

v2v1

DS2

VSC2

DC ring

DFIG-based wind farm

DS1

Pab

Pcd

PdePef

Pfa

a

b

c

d

e

f

Pba Pbc

Pcb

Pdc

PedPfe

Paf

VSC1

VSC3

VSC4

VSC5

v5

v6

BESS

Micro-grid 2

9/19/18

VSC type EDC(p.u.) ma

φ(deg)

LTC tap Ploss (MW)

VSCSlack 1.0000 0.8721 -13.3660 1.0354 0.0718VSCPsch 0.9952 0.8151 3.7648 0.9970 0.0066VSCPass 0.9955 0.8842 0 1.0113 0.0281VSCPass 1.0006 0.8612 0 1.0014 0.0571VSCPass 0.9976 0.8824 0 1.0113 0.0282Convergence: ε= 10-6 takes 5 iterations and ε= 10-12 takes 6 iterations

VSC typeEDC (p.u.)

maφ

(deg)LTC tap Ploss (MW)

VSCSlack 1.0000 0.8721 -13.3660 1.0354 0.0718VSCPsch 0.9952 0.8151 3.7648 0.9970 0.0066VSCPass 0.9955 0.8842 0 1.0113 0.0281VSCPass 1.0006 0.8612 0 1.0014 0.0571VSCPass 0.9976 0.8824 0 1.0113 0.0282Convergence: ε= 10-6 takes 5 iterations and ε= 10-12 takes 6 iterations

DC cables PDC (MW) Ploss(kW)send-rec rec-send

a b 1.6616 -1.6582 3.4514b c 2.1582 -2.1523 5.8467c d -0.3476 0.3477 0.1143d e -5.3908 5.4183 27.4889e f 2.4531 -2.4456 7.5132f a -2.5975 2.6038 6.3563

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Smart Grids

9/19/18

AC Smart Grid

9/19/18

§ According to the philosophy put forward by the academician Amin and Wollenberg from the University of Minnesota, a good starting point to endow the electrical power grid with a degree of intelligence and not only the reflexes provided by today’s advanced protection systems, is to embed independent processors with a robust operative system, in each component, in each substation, in each power plant

§ These processors or agents must be connected to sensors located in the component itself or in the substation in order to assess its status of operation continuously and to report it to the neighbouring agents through the associated communication circuits. This processor agent is the kernel of the smart grid

How to Endow the Electrical Power Grid with a Degree of Intelligence?

Interruptor

Agent

Power cable

Communication channelSeñales censadas

Communication port

Communication port

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§ One of the big challenges facing power grid operators is the so-called blackouts§ It is thought that substation intelligence should be able to ameliorate this

problems. If the power grid were to develop a fault that were to lead to islanding operation and a possible blackout , the communication grid and processor agents would remain intact and able to balance the demand-generation requirement, in an almost instantaneous basis

How to Endow the Electrical Power Grid with a Degree of Intelligence?

B

Isla 1

Isla 2

B

9/19/18

Communications Infrastructure and Protocols for Smart Metering

§ A Typical communications infrastructure for smart metering has threecommunications interfaces: Wide Area Network (WAN), NeighbourhoodArea Network (NAN) and Home Area Network (HAN)

§ A HAN uses wired or wireless communications and networking protocols toenable the interoperability of networked appliances and the interface to aSmart Meter. It includes mechanisms to protect consumer data and themetering system

NAN Smart Meter

Smart appliances

Micro-generation

EVCharger

Energy Storage

HAN

ZigBee is based on the IEEE's802.15.4 personal-area networkstandard. It is an alternative to Wi-Fiand Bluetooth for some applications,including low-powered devices,which do not require a lot ofbandwidth, such as smart sensors

9/19/18

Communications Infrastructure and Protocols for Smart Metering

§ The NAN is charged with transferring the individual consumption readings ofSmart Meters; however, when the Smart Grid is fully developed, the NANshould enable continuous diagnostic messages and real-time messages for thepower system operation support

§ For metering, it is estimated that a household will require less than 100 kBper day and a firmware upgrade may require 400 kB of data to be transferred.The communication technology used for the NAN, such as Zigbee, has a datatransfer rate of 250 kB/s. However, the situation will change drastically ifreal-time or near real-time Smart Grid functions are added

NANSmart Meter

Smart Meter

Smart Meter

.

.

.

.

.

.

Data concentratorWANGateway

Meter data management

Network operators

Energy suppliers

Other actors

HAN

HAN

HAN

9/19/18

State Estimation§ Measurements are collected and fed into a state estimation program. A

measurement z may be seen to be a function h of one or more state variablesx1, x2…. However, there is general agreement that a measurement neverdisplays the exact value and that instead, they represent a result within acertain range of confidence.

§ In a system with more than one simultaneous measurement, each measuredvalue can be seen as the actual value with an associated, unknown, error e.

§ Extrapolating this to a set of m measurements in a system with n statevariables, yields following, generic result:

9/19/18

Test Case§ An AC medium-voltage µgrid with distributed AC and DC DERs. Tom

Rubbrecht, On the State Estimation of Three-Phase Micro-grids withDistributed PV Generators, MSc Thesis, Tampere University of Technology,Tampere, Finland, June 2016

9/19/18

Three Phase Power Flow SolutionsVM (p.u.) Phase A Phase B Phase C

Node 1 1.0500 1.0500 1.0500

Node 2 1.1000 1.0971 1.0972

Node 3 1.0980 1.0974 1.1006

Node 4 1.1664 1.1661 1.1679

Node 5 1.0936 1.0926 1.0894

Node 6 1.1053 1.0982 1.0884

Node 7 1.0933 1.0923 1.0891

Node 8 1.0723 1.0746 1.0800

Node 9 1.0915 1.0929 1.0986

Node 10 1.0908 1.0985 1.1108

Node 11 1.0912 1.0926 1.0983

Node 12 1.1022 1.0995 1.1035

Node 13 1.1124 1.1095 1.1035

Node 14 1.1255 1.1227 1.1268

Node 15 1.0986 1.0963 1.0973

Node 16 1.1187 1.1085 1.1135

VA (deg) Phase A Phase B Phase C

Node 1 0.0 -120.0 120.0

Node 2 -7.2656 -127.4895 112.5715

Node 3 -7.9506 -128.1517 111.8248

Node 4 -10.7687 -130.9733 109.0228

Node 5 -8.1344 -128.2761 111.4854

Node 6 -13.1550 -133.8973 105.2256

Node 7 -8.5975 -128.7393 111.0222

Node 8 -8.3380 -128.5909 111.3568

Node 9 -14.5717 -134.2091 106.3837

Node 10 -8.8012 -129.540 110.8937

Node 11 -7.7035 -127.9063 123.9680

Node 12 4.1815 -115.9593 121.1035

Node 13 -8.1858 -128.3885 111.6280

Node 14 -8.0551 -128.2163 111.6380

Node 15 -12.5842 -133.2800 106.8423

Node 16 -6.4030 -126.5639 113.2903

DC nodes 17 18 19 20 21 22 23

EDC 2.1452 2.0004 1.8771 1.8775 1.9293 2.0000 2.0000

DC nodes 17 18 19 20 21 22 23

ϕ -13.4756 -9.2015 -9.5163 -8.8507 -5.0486 -14.2040 -4.3533

9/19/18

Three Phase State Estimation SolutionsVM (p.u.) Phase A Phase B Phase C

Node 1 1.0499 1.0457 1.0576

Node 2 1.0980 1.0869 1.0943

Node 3 1.0951 1.0873 1.0952

Node 4 1.1680 1.1629 1.1654

Node 5 1.0892 1.0798 1.0837

Node 6 1.0970 1.0788 1.0750

Node 7 1.0849 1.0758 1.0745

Node 8 1.0869 1.0821 1.0905

Node 9 1.0843 1.0797 1.0928

Node 10 1.0869 1.0758 1.0791

Node 11 1.0996 1.0897 1.0987

Node 12 1.1130 1.1081 1.1217

Node 13 1.1286 1.1259 1.1371

Node 14 1.0945 1.0847 1.0915

Node 15 1.1121 1.0919 1.1006

Node 16 1.1433 1.1370 1.1387

VA (deg) Phase A Phase B Phase C

Node 1 0.0 -120.0 120.0

Node 2 -7.8712 -128.2322 112.1799

Node 3 -8.6935 -128.9892 111.3769

Node 4 -11.7596 -132.3128 107.9810

Node 5 -8.8034 -129.2025 111.8042

Node 6 -14.0577 -135.2617 104.6870

Node 7 -9.8507 -130.5558 110.5431

Node 8 -9.1934 -129.4744 110.9344

Node 9 -15.7744 -135.4127 105.6966

Node 10 -10.6496 -130.4787 110.0098

Node 11 -8.4110 -128.7196 111.6721

Node 12 3.9248 -116.2479 103.2365

Node 13 -8.0656 -128.4333 111.4425

Node 14 -8.7638 -129.1297 111.2124

Node 15 -13.4665 -134.5451 106.2696

Node 16 -7.4227 -127.8898 112.7109

DC nodes 17 18 19 20 21 22 23

EDC 2.0031 1.8435 1.8470 1.9940 1.9828 2.0044 1.9922

DC nodes 17 18 19 20 21 22 23

ϕ -15.0865 -11.4386 -11.1997 -8.8297 -6.6137 -15.8607 -5.9590

9/19/18

VSC-HVDC Systems With High Temperature Superconductor Cables

GDC

EDCR EDCI

PDCRvRV vIV

aRm aIm

Rectifier InverterPoint-to-point

EDC

PDCvRV vIV

aRm aIm

Rectifier InverterBack-to-back

DC Grid

DS

MG1

MG2

GDC2

GDC1

GDC3

VSC1

VSC2

VSC3

Meshed multi-terminal VSC-HVDC system

DC Bus

DS

MG1

VSC1

VSC2

MG2

VSC3

Back-to-back multi-terminal VSC-HVDC system