Distributed Control of AC/DC Microgrid Voltage Containing EVs · Distributed Control of AC/DC...

Distributed Control of AC/DC

Microgrid Voltage Containing EVs

Meiqin Mao

Hefei University of Technology

2019-08-10 2019 Fort Collins Symposium on Microgrids 1

Outlines

2019-08-10 2019 Fort Collins Symposium on

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2

Current status of electric vehicles

Introduction

Annual sales of EVs In China

Ten thousand Million

(2015-2040)Annual sales volume and forecast of global vehicle

EVs sales

Total vehicle sales


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Introduction

Challenges of EVs integration into power system

large-scale EVs integration

Disordered charging

Voltage fluctuations

Frequency fluctuations

Gird harmonic

distortion

Other

problems


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Introduction

AC&DC hybrid microgrid

Higher efficiency

Better Expandability

More reliable


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Outlines


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Relationship between Voltage Deviation and Power Increment in AC-MGs

= =

P P

P θ M Nθ U

Q Q Q U / U K L U / U

θ U

Δ Δ Δ

Δ Δ Δ

Higher R/X in MGs

0; 0M L

In MGs:

1

= ( sin cos )

= ( sin cos )

ij i j ij ij ij ij

N

ij i j ij ij ij ij

jj i

M U U G B

M U U G B

=

−

− −

( sin cos )ij i ij ij ij ijL U G B = − +

=

−=

N

ijj

ijijijijjij BGUL

1

)cossin(

1

1

−

−

=

=

U / U N P

θ K Q

Δ Δ

Δ Δ

Relationship between voltage and power incensement in AC&DC-HMG


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Relationship between voltage and power incensement in AC&DC-HMG

Different from AC-MGs, the line of DC-MGs is only of the resistance characteristics

1/ − = U U N P

Thus, are mainly related to in the AC-MGs and DC-MGs

ΔU

ΔP

Relationship between Voltage Deviation and Power Increment in DC-MGs

1

1

11 12 11

2

21 22 112

2

1 24

Δ

...ΔΔ

...Δ

... ... ... .........

...ΔΔ

n

n n nn

n

n

U

UN N NP

UN N NP

U

N N NPU

U

=

The EVs are used as active power units to regulate the bus voltages

This paper:


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Outlines


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Distributed voltage regulation

algorithm

Centralized algorithm

DG

DG

DG

DG

DG

MGCC

1.Central controller.

2.High communication burden.

3. Communication period is longer.

4. Lower expandability.


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algorithm

Decentralized algorithm - Gossip Algorithm

Local computer 1

Local computer 3

Local computer 5Local computer 4

Local computer 2

1.No central controller

2. Point to point

3. Multiple iterations


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algorithm

Objective Function

2 2

REF

1 1

( ) ( ( ) U )N N

i i

i i

minF U U= =

= = − ΔP

voltage deviations

voltage magnitudes

power increments

maximin i iU U U

maximin i iP P P

s.t.


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algorithm

Solution of the Proposed Model

( )

. . ( ) 0, 1,...j

min F x

s t g x j m =

By the penalty function method2

1

}))(,0(min{' =

+=

M

i

igFF x

1'

2F = +T Tx Hx c x

quadratic function

1−= −x* H c

optimal solution


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algorithm

Solution of the Proposed Model

k k k= U P Cc U + P + C&

constant matrices

N* 1 U P C

1

(k k k C )*

i ij ij j ij j ij j

j

x P H U P−

=

= = + +1−= −x* H c


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algorithm

Distributed Voltage Regulation Strategy for AC&DC-HMG

Voltage regulation processing : ◆ Internal regulation

◆ unified regulation 2019-08-10 2019 Fort Collins Symposium on

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algorithm

The whole voltage regulation processing

Stage 1: Each MG regulates its

voltages by distributed voltage

regulation algorithm.

Stage 2: There are six cases of

the second stage voltage

regulation.


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algorithm

Six cases of the second stage

Six cases of the second step

Different cases correspond to different solutions.

Scenarios AC-MG voltages

EVs’ scheduling capacity

AC-MG voltages

EVs’ scheduling capacity

Case 1 ---- ----

Case 2 Enough Not enough

Case 3 Not enough Not enough

Case 4 Not enough Enough



5%

5%

5%

5%

5%

5%

5%

5%

5%

5%

5%

5%


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Outlines


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Microgrids topography

AC BUS0.4 KV

AC BUS0.4 KV

DC

AC

Bi-directional AC/DC

EV1

EV2

DC BUS0.75 KV

DC BUS0.75 KV

DC

DC

DC

DC

BT

PV

WT

PV

EV5

8

9

10

11

12

1314

16

20

21

22

23

2425

2627

15

17

18

19

EV3

32

1

7

6

5

4

EV4

Load

LoadLoad

Load

Load

Load

Simulation results and discussion


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Parameter setting Initial voltages

The initial voltages of AC-MG and DC-MG are mostly over limits


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Case 1

After voltage regulation for the first

stage, the voltage fluctuation is

within ±5%

1

2

3

0.1843

0.1056

0.95

EV

EV

EV

P MW

P MW

P MW

= −

= −

= −


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Case 2

After the first stage regulation, the node voltages are still mostly over the limits in DC-MG.

The solution of case 2 is launched.

Case 2*


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Case 2*

By using the scheme for case 2, the voltage regulation coordinated within AC-MG and DC-MG for the second stage is launched.

1

2

3

0.0931

0.8

0.45

0 1

0

4

5

EV

EV

EV

P MW

P MW

P MW

= −

=

= −

Optimal power of EV nodes


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Case 4After the first voltage regulation stage, there are still some node voltages over the limits in AC-MG.

The solution of case 4 is launched.

Case 4*


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Case 4*

By using the scheme for case 4, the voltage regulation coordinated within AC-MG and DC-MG for the second stage is launched

1

2

3

0.00956

0.1355

0.1566

EV

EV

EV

P MW

P MW

P MW

= −

=

= −

Optimal power of EV nodes


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Conclusions

➢ By the proposed method, the voltage deviation of the AC&DC-HMG can be stabilizedwithin 5% with power coordination between AC-MG and DC-MG with EVs connectedthe related nodes.

➢ In addition, each node regulates its voltage based on communication only withinneighboring nodes, thus reducing the burden for communications.

Future works

➢ We only considered the grid connection situation, and did not consider the situationwhen the EVs was connected in the island mode.

➢ The scheduling of electric vehicles can be optimized.


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Thank you!


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Distributed Control of AC/DC Microgrid Voltage Containing EVs · Distributed Control of AC/DC...

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