Mô hình hóa và điều khiển thiết bị kho điện sử dụng siêu tụ

October 28, 2014 Abstract Wind power is one of the renewables energy resources that help to lower the global warming trend Unlike a of wind fluctuation, the connection of a wind turbi

Modeling and Control of Supercapacitor Energy Storage Systems

M6 hinh hoa va dieu khien thiet bi kho dien sii dung sieu tu

Pham Tuan Anh'-^, Vu Hoang Phuong', Nguyen Phung Quang'*

'Hanoi University of Science and Technology - No I, Dai Co Viet Sir., Hai Ba Ti-ung, Ha Noi, Viet Nam

^Vietnam Maritime University - No 484, Lach Tray, Ngo Quyen, Hai Phong

Received: April 07, 2014; accepted October 28, 2014

Abstract

Wind power is one of the renewables energy resources that help to lower the global warming trend Unlike a

of wind fluctuation, the connection of a wind turbine to a grid (especially in islands where the grids are weak) could create severe problems to the transmission line designed for constant power and to the power system power conversion system which has the ability to provide the positive response of fast-dynamic energy storage for high power requirement in order to smooth out the output to eliminate rapid power oscillations on the grid This paper focuses on a Supercapacitor Energy Storage System (SCESS) in terms of modeling and the proposed control scheme is validated by simulations

Keywords: Supercapacitor Energy Storage System (SCESS), Bidirectional DC-DC Converter, Voltage Source Inverter, Active Rectifier

Tom tat

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1 Introduction generators The main issues of using the ESS to

smooth out output power include ESS topology and The principles of a wind turbine are shown in

Fig 1 A wind energy conversion system transforms

wind kmetic energy mto mechanical energy via rotor

capacity requirement, converter control, ESS power reference setting, etc Different types of ESS have blades This energy is then converted into electrical « u i ' J - ' ^ '

, „ ' ' - ' , flywheels, superconductmg magnetic energy storage, energy by different types of generators suoh as ^,^ ^^^ ^^^ ^_._._^ ^^^^.^ ^^ Supercapacitors

doubly-ted induction generators and permanent ^ c^, - ^ • u i- u i:

•' , , "= ^ „ represent one or the newest innovations m the tield or magnet-excted synchronous generators Power ^ j ^ ^ ^ ^ ^ , ^ ^ , ^ ^ _^ ^ ,^^

converters are responsible tor transformation or , ^ - j L „ -T-I c,-^ u i

, ^ ^ , between capacitor and battery The SC has large

electrical energy, makmg it suitable for the electric t r - u J - L ^•'J, • 1, u- h fl • f capacitance, excellent instantaneous charge-discharge grid One area of concerns is the high fluctuation of

varying wind speed The frequency fluctuation and

performance, higher power density (but lower energy density) and longer life cycle than battery [3] The SCESS might be integrated to DC-bus some power quality problems threaten the security ,, j , ^ A / ^ J H J * , - I J

, , r- J • :, called DC-coupled or AC-side so called AC-coupled and stability oi power system caused by wmd cannot _ cz-r-nc i u L - J

, _, T, , , • _, , so that the SCESS can exchange both active and

be ignored Ihe problem mentioned above can be ^ •.! .u - J •

, , , '^ , , , , reactive power with the wmd power system aim to

solved by equipping the wind power system with an ^ ^ „ „ , ^ „^t t^^ „ , „ a power fluotuations and

energy storage system (ESS) to absorb or supply ^ , ^ y , j ^ ; ,^^ ^ , ^ , ^^^

power to compensate the fluctuated output from the - , r u- ^

t^ f f The purpose of this paper is to suggest a new

effective and simple confrol scheme o f t h e SCESS in

• Corresponding author: Tel (+84)4 3868.3518 order to achive rapid response of both active and

Q Conlrol)

_ _ _ _ _ _ _ ; _ ^ _ <v«UraQru_ _

' _ _ _ _ _Si^efwsqiy ConBp/_ _ _ _ _ General wind turbine control structure with the SCESS

Supercapacitor

Pack

F i g 2 Topology ofthe SCESS The SCESS is based on a diree-phase PWM

voltage source inverter (3PVSI) connected between

connected to the DC link through a non-isolated

bidirectional DC-DC converter (NBDC) Active

power (P) is injected or absorbed by SCESS from the

line to smooth out the intermittent wind power by

charging or discharging the supercapacitor Reactive

power (Q) regulation is related to the characteristics

of each grid The Q requirement can be given in three

different way: Q-set point, power factor control,

voltage conttol [4, 5],

2 Modeling o f t h e SCESS

Fig 2 represents the SCESS connected to the

grid In our study, the power stage is made up of an

3PVSI and an NBDC The NBDC consists of a

parallel combination of an unidirectional buck and an

unidirectional boost converter The current can be

either drawn from or injected into the DC-link by the

operation mode It is required to ensure the power

balance between the primary power source

-Supercapacitor and the load by regulating the DC link

voltage to a fixed value The confrol o f t h e 3PVSI is

not only just keeping the constant DC link voltage, but also satisfy one of three requfrements: Tracking the Q-setpoint, maintenance the power factor of the SCESS, regulate the voltage at the point of common coupling Internal current and voltage loops in both converters are used

2.1 Modeling ofthe NBDC with supercapacitor

Each converter is composed of an IGBT and a

diode making up a bi-positional switch of the power-pole The equivalent series resistance o f t h e DC link switching power-pole, the positive inductor current as

the IGBT SBK and the diode DBK associated with the

buck converter take part Similarly, the negative inductor current represents discharge mode, where

only the IGBT SBS and the diode DBS associated with the boost converter in action In our approach, instead

confrolled complementarily by means of

9, 9 (defined in Fig 3 and the converter always operates in current continuous conduction mode

The current flow direction of the inductor is the

same as the super capacitor charging power flow

dfrection There is a threshold duty cycle so called

Fig 3 Operation principle of NBDC

2.2 Modeling ofthe 3PVSI [6]

Dg that is calculated by Dg The duty

cycle d (defined in Fig 3 ) can control the current

flow direction as following: If d> DQ then inductor

averaged current should be greater than zero, charge

mode is activated (Fig 3 a), if d <DQ then inductor

averaged current should be less than zero, discharge

mode is occurred (Fig 3 b) The average

representation ofthe bidirectional described in Fig 4

IS an ideal ttansformer with a turns-ratio 1: d(t},

where d(t) represents the duty-ratio of the IGBT

associated with the charge mode:

'dit)„,

Three-phase PWM voltage source inverter has advantages as can not only stabilize DC-link voltage, but also can adjust the grid-side power factor, reduce the current harmonic distortion, energy can flow bidirectional The simplified model of 3PVSI connected to the gnd is shown in Fig 5 where:

ê,ê,ê are three-phase voltage sources; u^,Uf,,u^

are three-phase voltage for input side of 3PVSI;

^ấb'h are three-phase current of 3PVSI, L^ is the inductance of AC side; R^ is equivalent circuit resistance; C is DC-Link capacitor; R^^ is DC side equivalent load impedance; M^C is DC voltage, i^^ is

the current of DC system

Based on the topology and Kirchhoff s law we

can get equations (3) in three-phase stationary coordinate system

The averaged dynamic model of the NBDC is

given by (2) The averaged confrol input d is defined

as a sufficiently smooth function taking values in [0,

1]

dl

^du^

dl

-RL'Ị+''•'„

(2)

c'i'^6 '^^^^ ''"'^i^

'"'KJ^ '"^^ '"'K^ "\

Fig 5 Simphfied model of 3PVSI connected to the

grid

With Si the switching function defined by:

5, —1 (upper switch ON); S, ——1 (bottom switch

ON) with phase/ — a , 6 , c The mathematical model

given in (3) can be converted into the model in dq

rotary coordinate system through Park

transformation and the model is showed in (4)

(3)

e„

"» -",

ig

i^ " dl

i„

'' +

u„

"»

dt cc dc

^ dt ^ s i l

L—^^e„-RJ,-~LJL i.-u

^ dt * ^^ ^^ '

dt *

S^i —S^cosLtJt-^S^smiAjt

S^ = S^ cosw; — S^ sin ujl

1 (2S^~S,-SJ

(s.-s,)

Where, i^, i^ are three-phase current of 3PVSI

lli dq coordinate system; e^, e are three-phase

voltage of grid in dq coordinate system; Uj,u are

three-phase voltage for input side of 3PVSI in dg

coordinate system

3 Control scheme o f t h e SCESS

In our approach, there are two confrol structures

of NBDC and 3PVSI diat are shovm inFig 6 The

input signal to the NBDC is the high frequency

power mismatch which is given by outer loop control

so called "Energy management Algorithm - EMA"

EMA will not be discussed in this paper Instead, step signal will be used to generate the supercapacitor reference current, and is then compared with the actual supercapacitor current to produce the switching signals for the NBDC

Voltage Oriented Confrol (VOC) technique of 3PVSI is chosen The confrol system is dual-closed-loop confrol structure which adopts an outer voltage loop and an inner current loop The outer voltage loop

is used to guarantee the stability of the system, and

rapid response

The inner loop current controllers were designed based on the Bead-beat method as described in [5, 7]and the outer loop DC-link voltage confroUer was tuned with PI structure usmg the "symmetrical optimum" principle as described in [4]

When designing the inductor current control loop, suppose that the DC-link voltage M^^- has significantly slower variations than the inductor current i^

Moreover, if the overall conttol goal is fulfilled,

the DC-lmk voltage u^^ should remain constant So

the only conttol variable ofthe NBDC conttol system

is /^ , the conttol variable « ^ is taken care by 3PVS1

By linearizing the first equation of (2) around a quiescent operating point (w^^ is constant) one obtains

L^ = -RX+dU^^ (5)

The fransfer fimction relating the inductor current with the duty ratio vanations is computed sfraight forwardly:

GA^) = (6)

If one considers that f 7 ^ = « ^ (the confrol

goal is fulfilled by 3PVSI conttoller), then the plant is invariant with the operatmg point Furthermore, consider a PI controller o f t h e NBDC plant such that

the inductor current follows its reference if Because

the inductor current plant is ffrst order, PI confroUer may be effectively used to ensure both zero steady-state error and conttolled bandwidth By choosing the current confroUer as:

i^

L SBKISBS T

Generator

NBDC control structu re

1

ui*Ji(_Q

• /

ENERGY

MANAGEMENT

ALGORITHM

G,.L Fig 6 The control stmcture ofthe SCESS

Table 1 Simulation parameters (7)

The closed-loop transfer function ofthe inductor

current confrol loop turns out to be (8), Suppose that

the inductor current closed-loop dynamical

performance is described by the bandwidth 1/7^^

and a convenient damping coefficient ^g^ (e.g., 0.7)

UDC-I,.k Cdc CsCESS C,ji ESR„ii

700V

1000 uF 10.75F 5SF 0.022 Ohm

N,.„,

N,.„,i.i ESRsCESS Uccll

42

8 0.1155 Ohm 15V

GcL T.r 5-1-1

(8)

^pC-^C

Expression (9) allows identification of confroUer

parameters that satisfy the desired performance

:« - - ^ ^ ^

'ic ~ 2?oc 'oc „

,2 2?0C 'oc

j2 (9)

'^C 'IC

4 Simulations

4.1 Simulation Parameters

A simulation model was built and parameters

were shown in table I The numerical simulations are

carried out with Matlab/Simulink/SimPowerSystems

The supercapacitor block in SimPowerSystems is a

generic model parameterized to represent most

popular types of supercapacitors The block employs

Stern equation and Tafe! equation as in [8]

Fig 7, Inductor current response

4.2 Simulation Results

One of the key variables in the overall system performance was the active power exchange (proportional to the inductor current of the NBDC and the direct current component of VSI as well) between SCESS and the grid Thus, its value had to

be tightly confrolled Fig 7 shows the inductor current response to a step-change illustrated the

discharge mode (Negative inductor current value)

Fig 8 and Fig 9 show the performances ofthe 3PVSI While active power is exchanging (SCESS alternated between charge mode and discharge mode), the voltage o f t h e DC link were kept constant

as shown in Fig 10 The three-phase components: voltage and current ofthe SCESS is shown inFig 11 Fig 12 explains the dynamic performances of the supercapacitor during charging and discharging process m terms of voltage, current and energy

(state-'.<*

F i g 8 dq components ofcurrent response of 3PVSI P ' S - ' • ^^tive Power exchange response o f t h e

SCESS

Fig 10 DC link voltage response Fig I I Three-phase voltage - current of SCESS

^-.^

?

>"

i es

• ^ :

1 ^ "^ 1

^"

'

1 V

1 1 1

i-—, J

r—'*' ' 1 V i j

Fig, 12 Dynamic performance ofthe supercapacitor system

5 Conclusion

Active power flow confrol is the most essential

conttol loop which permitted us to integrate the

SCESS to the wind turbine so that to mitigate the

power fluctuation It can be observed that the tracking

performances of the tuned confrol loops closely

follow the references We can confirm that the

proposed conttol scheme of the supercapacitor ESS

which consist of a NBDC and a 3PVSI has

successfully applied in active power conttol create

good condition to develop a proper energy

management algorithm which will be discussed in

another paper

References

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Technologies For the integration of fluctuating

renewable energy," University ofLimenck, 2009

[2].M Stiebier, "Wind Energy Systems for Electric Power

Generation," 2008 Springer-Veriag Berlin Heidelberg,

2008

[3] F 0 B'eguin and E z F ackowiak, Supercapacitors

Verlag GmbH & Co KGaA, Boschstr 12, 69469 Weinheim, Germany, 2013

[4] M L P R Remus Teodorescu, "Grid Converters for Photovoltaic and Wind Power Systems," ed: John Wiley & Sons, Ltd ISBN: 978-0470-05751-3,2011

[5] N P Quang and J.-A Dittrich, "Vector control of three phase AC machine- System Development in the

Practice," Springer Berlin - Heidelberg 2008

[6].M Malinowski, "Sensorless Control Strategies for

Three - Phase PWM Rectifiers," Ph.D Thesis, Warsaw University of Technology 2001

[7].Q WEN, L ZHU, and C FU, "Research on deadbeat Current Contto! Sttategy of Three-Phase PWM Voltage

Source Rectifier," Proceedings ofthe 2nd International Conference on Computer Science and Electronics Engineering (ICCSEE 2013) 2013

[i] Supercapacitor Available:

http://www.niathworks.com/help/physmod/sps/powersy s/ref/supercapacitor.htmlJsessionid=lac990ceb44fF(26 4735cdla7abb