Djagarov_EEEIC_2012

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Investigation of Multi Input Adaptive

Control for STATCOM

Nikolay Djagarov

Technical UniversityElectrical Equipment and Power

SupplyDepartment

Varna, [email protected]

Zhivko Grozdev


SupplyDepartment


Milen Bonev


SupplyDepartment


Abstract In the present report is presented the advanced

adaptive control of static compensator (STATCOM) consisting of

conventional PI-regulator and multi input adaptive regulator.

The adaptive static modal regulator identifies the controlled

object by optimal observer in real time. By means of identified

parameters and variables of controlled object is calculated thecontrol signal. The operation of power system connected through

transmission line into infinity buses is being investigated. The

power system consists of generator units, static and dynamic

loads and STATCOM. The results from investigations show the

effectiveness of suggested advanced adaptive control.

Keywords-component; STATCOM, FACTS, adaptive control,

singular adaptive observer

I. INTRODUCTIONThe development and improvement of powerful

semiconductor technology in recent years contribute to the

development and implementation of flexible alternate currenttransmission systems (FACTS). The FACTS devices representa group of innovative devices based on power electronics

which are used primarily in high-voltage transmission lines.These devices perform dynamic compensation of powersystems by improving natural characteristics of transmissionlines, increasing the transmission power and governing theform of voltage lines.

The static synchronous compensator represents shunt

connected static compensator which generates or absorbsreactive power in order to maintain or adjust the parameters of

the power system [1,2,3,4].The main advantages of static synchronous

compensators are:- Voltage control under different operating modes;- Reactive power control;- Improving the power system stability in energy

transmission at long distance;- Improving insensitivity of the network by controlling

the voltage during major disturbances, such as. shortcircuit;

- Improving the reliability of power systems;- Reducing the costs and increasing capabilities of the

managing controllers.

For control of FACTS are used all known methods fromthe theory of control: classical PI-regulators, methods of fuzzylogic and neural network, regulators with adjusted parameters,

regulators with variable structure and others. The main trend isto make these controllers adaptive [5].

However, this relates to the need of large computationalresources, which will worsen their performance and hence -the quality of regulation.

The adaptive stabilizer suggested by us uses optimal

singular adaptive observers [6]. These observers based onmeasured parameters of the controlling object identify the

parameters and variables of minimal model of Frobenius. Themain difference of this identification from the known is thatnot only the current vector is estimated but also the initialvector. This avoids iterative solution of Riccati equations andhence is achieved very high speed of identification andcalculation of control signal. Thanks to this, the calculationtime of the control signal and feedback is negligible small incomparison with the speed of running processes in the system.

Therefore, these regulators improve all parameters of thetransition process, damping the oscillations and improvingpower system stability as whole.

II. STUDIED POWERSYSTEMOn Fig.1 is presented studied power system including

infinity power system, transmission line, static active-inductive load, dynamic load and STATCOM connected toload bus.

The suggested STATCOM represents GTO-based multi-level voltage source converter (VSC) connected in parallel with

power system by coupling transformers. The four sets of three-phase voltages obtained at the output of the four three-levelinverters are applied to the secondary windings of four phase-shifting transformers (with phase shifting 7,5). In this wayof connecting of power transformers are neutralized the oddharmonics up to 45th harmonic with exception of 23rd and 25th(which is ideal for balancing of power system). By regulatingof amplitude and phase of the generated voltage fromcompensator can be regulated the active and reactive powergenerated/absorbed to/from power system. Also by adjustingthe output voltage amplitude of the compensator can beregulated the reactive power flow and voltage of the line. On

This article is published with help of project BG051PO001/3.3-05-001Science and Business, sponsored by operative program Development ofHuman Resources from European Social Fund.


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the other hand the DC-voltage of capacitors controls thegenerated voltage of compensator output. In this way forchange of reactive power flow of STATCOM the controller ofthe compensator first must temporary absorb reactivepowerfrom power system for charge the power capacitors. This activepower flow is controlled by managing of firing angle of GTO-thyristors [7]. of pagination anywhere in the paper. Do notnumber text heads-the template will do that for you.

On the Fig.2 is presented circuit diagram of one 3-level

GTO-bridge converter module, with limbs R, S and T. Withthe capacitor centre tap Nconnected through diodes, each acnode has three voltage levels, +0,5Udc, 0, and -0,5Udc. Thecapacitor voltages are regulated and equalized at 0,5Udc byanother DC-voltage feedback regulation loop and an innerDC-voltage equalization feedback loop [8]. The phase voltage

at the AC-terminalR,ERN1 with respect to the capacitor centretap, is determined by the ON and OFF states of the fourswitches GR1, GR2, GR3 and GR4.

III. CONTROL OF STATCOMThe control of compensator consist from three control

loops; adaptive voltage regulator; current regulator; DC

regulator. The basic idea of STATCOM control is keeping the

amplitude of voltage in connection node close to the referencevalue, which is given from operator.

The structure of the STATCOM control is shown in Fig.3.The voltage of connection node UT and the current ofcompensatorIS are measured. The inner current control loopforces the voltage source converter to behave as a controlledcurrent source. For connection of STATCOM to present nodeis used power transformerTr. The node voltage is controlledby a two input adaptive controller and gives the referencesignal for the q-current controller. To regulate theDCvoltageof the outer control loop to its constant value a PIcontroller isused. To design the PIcontroller parameters, the inner controlloop is modeled as a first order delay element and the dynamics

of theDClink are taken into account. The controller is tunedwith the symmetrical optimum [9]. The inner current control isperformed with PI-controllers in rotating dq-axes coordinates.Grid synchronization is done with a PLL algorithm.

The basis of the adaptive regulator, which regulatesvoltage of static synchronous compensator, is that in real timeit can continuously identify the controlled object by linealmodel from low order and after that it creates the controlling

signal. The performed numerous investigations [10] show thatfor the needs of regulator can be used models from 2nd order.

This provides very high performance and accuracy. In the

Fig.1. Diagram of studied power system

Static loadTransmission

line

Power

System

48 GTO

Firing pulses

IM

Dynamic load

STATCOM

Controller

STATCOM

Fig.2. Three level diode - clamped converter.

R

UR

UDC1

UDC2

UDC

+

+

+

-

-

-

S T

US UT N

GR1

GR2

GR3

GR4


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i

iib.Ahb

)

+= (14)

where: [ ]21 ii bb=ib

The estimation of initial vector ( )0x is calculated by theoptimal estimator of following type:

( ) *3 b.Yx 0 = (15)

where: [ ]02013 UU = ; [ ]T2T1*T bbb))

=

The current vector is estimated by the degenerate OSA

observer of the following type:

( ) ( ) ( )kkk .uBx.Ax 11 ++=+ (16)( ) xx 00 = ; k=0,1,2,

The investigations have shown that controlling system

can be identified with the help of model from second order i.e.

2n =

( ) ( ) 2211 x.ax.a == px.apIt

qref (17)

where: p=k, k+1, k+2

IV. SIMULATION STUDYTo prove of rightness and effectiveness of studied

system work a computer model of suggested system and

control was created inMATLAB space. Different disturbances

causing transient processes have been simulated. The

simulated transient processes are: three-phase earth short

circuit and its disconnection from circuit breaker,

connection/disconnection of powerful static active-inductive

load, connection/disconnection of powerful dynamic load.

The obtained simulations are compared with system of

identical parameters in with conventional control (PI-controller) for STATCOM. The following figures show some

typical parameters of investigated power system. On the

figures: STATCOM with adaptive two-input controller-blue

line with PI-controller-red line.

First transient process (Fig.4Fig.7) which was issimulated present three-phase earth fault at time 5sec and its

Fig.4. Voltage of STATCOM buses

UT [p.u.]

5 5,05 5,1 5,15 5,2 5,25 5,3

0.99

0.995

1

1.005

1.01

time [sec]

Fig.5. Reactive power of STATCOM

QSTATCOM [MVar]

10 10.05 10.1 10.15 10.2 10.25 10.3 10.35

-60

-40

-20

0

20

40

60

80

100

time [sec]

Fig.6. Firing angle for GTO-thyristors

G [deg]

5 5.05 5.1 5,15

-20

-10

0

10

20

30

40

50

time [sec]

Fi .7. Current of STATCOM

ISTATCOM [p.u.]

5 5.05 5.1 5.15 5.2 5.25 5.3 5.35 5.4

0

0.5

1

1.5

2

2.5

3

3.5

time [sec]


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disconnection from circuit breakers for time 5,03sec. Parts of

parameters of STATCOM and power system are shown

below.

Second performed transient process (Fig.8Fig.13), presentconnection at 1,5sec and disconnection of powerful dynamicload. Parts of parameters of STATCOM, power system anddynamic load are shown below.

Fig.8. Voltage of STATCOM buses

UT [p.u.]

1.5 1.6 1.7 1.8 1.9 2 2.1

0.92

0.94

0.96

0.98

1

1.02

time [sec]

Fig.9. Reactive power of STATCOM

QSTATCOM [MVar]

1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4

-100

-50

0

50

100

time [sec]

Fig.10. Firing angle for GTO-thyristors

G [deg]

1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

10

-5

0

5

10

time [sec]

Fig.11. Control current of STATCOM

Iqref

[p.u.]

1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

time [sec]

Fig.12. Voltage of STATCOM capacitors

UDC [V]

1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

1.2

1.4

1.6

1.8

2

2.2

2.4

x 104

time [sec]


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V. CONCLUSIONIt is proposed new combined adaptive control of

STATCOM consisting of a conventional current regulator andtwo-input adaptive regulator on the basis of adaptive observer.Through the estimated variables and parameters of theidentification model is calculated the control signal in channel

for voltage regulation.

Conducted simulation studies show the effectiveness ofthe proposed adaptive management. At disturbances in thepower system from proposed diagrams is possible to observe:reduction the transition time; reduction the oscillation oftransition process; limitation the deviations of the parametersof the system; facilitation the work of STATCOM.

REFERENCES

[1] Song Y.H., Flexible ac transmission systems (FACTS). The Institution ofElectrical Engineers, London, 1999.

[2] Sao C. K., Lehn P. W., A Benchmark System for Digital Time-Domain

Simulation of a Pulse-Width-Modulated D-STATCOM, IEEE Trans. OnPower Delivery, Vol. 17, No. 4, Oct. 2002.

[3] Hingorani N. G., Flexible AC Transmission Systems (FACTS)

Overview, IEEE Spectrum, pp. 40 45, April 1993.

[4] Hingorani N. G., Gyugy L., Understanding FACTS: Concepts andTechnology of Flexible AC Transmission Systems, IEEE Press, 2000.

[5] Canizares C. A., Faur Z. T., Analysis of SVC and TCSC controllers in

voltage collapse, IEEE Trans. on Power System., Vol. 14, pp. 158-165, Feb.1999.

[6] Sotirov L. N., Selected chapters from modern control theory, Technical

university of Varna, Bulgaria,1998, 281pp

[7] C. Dufour, J. Belande, Real-time Simulation of a 48-Pulse GTOSTATCOM Compensated Power System on a Dual-Xeon PC using RT-LAB,

IPST05, Monreal, 2005

[8] Y. Chen, B, Mwinyiwiwa, Z. Wokmski and B.T. Ooi, Regulating andEqualizing DC Capacitance Voltages in Multilevel STATCOMs, IEEE

Transactions on Power Delivery, Vol.12, No.2. April 1997, pp.901-907.

[10] D. Schroder, Elektrische Antriebe 2, Regelung von Antriebssystemen,Springer, 2001.

[11] Djagarov N. F, Bonev M. B., Multi-input adaptive stabilizer for

excitation of synchronous generator, "Bulgarian Journal of Power

Engineering",6/7, 2000, pp. 2833.

Authors:

Nikolay Filev Djagarov,Technical University, 9010 Varna, Studentska1, ElectricSupply and Electrical Equipment Department, Bulgaria, tel:+35952383265; e-mail:[email protected]

Zhivko Genchev Grozdev,

Technical University, 9010 Varna, Studentska1, ElectricSupply and Electrical Equipment Department, Bulgaria, tel:+35952383345; e-mail: [email protected]

Milen Bonev Bonev,Technical University, 9010 Varna, Studentska1, Electric

Supply and Electrical Equipment Department, Bulgaria, tel:+35952383345; e-mail:[email protected]

Djagarov_EEEIC_2012

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