reactive power compensation in inverter interfaced...

Special Issue of International Journal of Power System Operation and Energy Management, ISSN (PRINT): 2231 – 4407, Volume - 1, Issue-3

12

Reactive Power Compensation in

Inverter Interfaced Distributed Generation

1Satyaranjan Jena & 2B.Chitti Babu 1Department of Electrical & Electronics Engineering, Hi-Tech Institute of Technology, Khurda, Odisha-752057, India

2Department of Electrical Engineering, National Institute of Technology, Rourkela, Odisha-769008, India E-mail : [email protected]

Abstract - The consumption of reactive power is stochastic in nature for the distribution system. This uncertain variation of the reactive power leads to 1) Variation of voltage at the point of common coupling(PCC) 2)Low power factor 3)low efficiency 4) improper utilization of distribution system and 5) loss of synchronism for a grid connected inverter based – distributed generation. Now a day’s distributed generation (DG) system uses current regulated PWM voltage-source inverters (VSI) for synchronizing the utility grid with DG source in order to ensure the grid stability. In this paper reactive power compensation based hysteresis controller and adaptive hysteresis controller is analyzed for inverter interfaced DG which can control the active and reactive power independently. The adaptive hysteresis controller can reduce the current harmonic at PCC considerably which ensures lower total harmonic distortion (THD). The performance indices include THD of the grid current, fast current tracking during steady state and transient conditions. The studied system is modeled and simulated in the MATLAB Simulink environment.

Index Terms-Adaptive hysteresis current control, distributed generation (DG), voltage source inverter (VSI), utility grid, total harmonic distortion (THD).

I. NOMENCLATURE

ILa,iLb,iLc : three phase grid current

ild,ilq : d and q axis current

ω : angular frequency

θ : transformation angle

Vd,Vq : d-q component of PCC voltage

Pref : reference value of active power

Vdc : dc-link voltage

Va,Vb,Vc : grid voltage per phase

fc : modulation frequency

L : line inductance

Vpcc : voltage at PCC

II. INTRODUCTION :

NDER the restructuring phase of the electric power industry, the traditional vertically integrated utility environment is inevitably being changed. The power system operation will become more competitive and many challenges will arise. Since it is a clean energy source, it has lower impact to the environment, and

never runs out, DG based on renewable and non renewable energy is a hot issue in today competitive market [1].

In conventional generation stations, the generators operate at a fixed speed and thereby with a fixed grid-frequency; however, the dispersed generation presents a quite different and challenging picture. For example, the voltage generated by variable speed wind power generators, PV generators and fuel cells cannot be directly connected to the grid. The power electronic technology plays a vital role to match the characteristics of the dispersed generation units and the requirements of the grid connections, including frequency, voltage, and control. Power electronics is an efficient essential part for the integration of DG unit to achieve high efficiency and performance in power systems [2].

One important part of the distributed system is its control. The control tasks can be divided into two major parts. 1) Input-side controller, with the main property to extract the maximum power from the input source. 2) Grid-side controller, which can have the task like, control of active power generated to the grid, control of reactive power transfer between the DPGS and the grid; control of dc-link voltage, ensure high quality of the injected power, grid synchronization [3]

Special Issue

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ATEGIES IN STEM

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S AND URRENT

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Reactive Power Compensation in Inverter Interfaced Distributed Generation


16

V. RESULTS & DISCUSSION

The section reveals the simulation results for hysteresis and adaptive hysteresis current control algorithm applied to three-phase mains connected inverter system. The studied model has been developed and simulated in the MATLAB/simulink environment. For simulation, the Dc-link voltage is taken 600V, and the grid voltage is 400V (L-L). the modulation frequency is taken 10KHz and the command value of power is set to 3.5Kw.

A. Steady State Analysis

Fig.7and 8 shows the steady state response of hysteresis and adaptive hysteresis current controller. In steady state the reactive power demand of the load is kept very small.fig.7 (e) and 8(e) shows that active power is equal to the input command value 3.5 Kw. The active power demand of the load is more than the command value. The deficit power to the load is supplied by the utility grid. fig.7(c) and 8(c) shows the load current (dotted line) and the inverter current per phase.

Fig. 7 : Simulation result of the steady-state response of hysteresis current controller (a) grid voltage at VPCC (b) grid current (c) Inverter output phase current and load current (d)Dc-link voltage (e)Reactive power(f)Active power(g) Quadrature component of inverter current.

Fig. 8 : Simulation result of the steady-state response of adaptive hysteresis current controller (a) grid voltage at VPCC (b) grid current (c) Inverter output phase current and load current (d)Dc-link voltage (e)Reactive power(f)Active power(g) Quadrature component of inverter current

Fig.9 shows the adaptive hysteresis band width for a constant load.

Fig. 9 : Adaptive hysteresis band

B. Transient Analysis Fig.10 and 11shows the transient response of

hysteresis and adaptive hysteresis current controller. In this reactive power demand of the load is increased between a period 0.08 sec to 0.14 sec. fig.10 (b) and 11(b) shows that the inverter current is increasing due to the increase of reactive power load demand.

Fig.10 : Simulation result of the transient response of hysteresis current controller (a) grid voltage at VPCC (b) grid current (c) Inverter output phase current and load current (d)Dc-link voltage (e)Reactive power(f)Active power(g) Quadrature component of inverter current

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-200

0200

Vol

tage

(V)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

500

Vol

tage

(V)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

5000

P(W

att)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-5000

05000

Q(V

ar)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-10

010

Time(Sec)

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-200

0200

Vol

tage

(V)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-10

010

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

500

Vol

tage

(V)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-5000

05000

P(W

att)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-5000

05000

Q(V

ar)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Time(Sec)

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time(Sec)H

yste

resi

s B

and

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-200

0200

Vol

tage

(V)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

500

Vol

tage

(V)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

5000

P

(W

att)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

5000

Q

(V

Ar)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Time(Sec)

Cur

rent

(A)



17

In described control scheme the PWM-VSI is able to inject the reactive power when the load demand increases which can be analyze by observing Fig10 (f) and 11(f).As far as the active power is concerned Fig 10(e) and 11(e) shows that the active power is almost constant and equal to the input command value (3.5Kw). Fig. 10(g) and 11(g) shows the quadrature component of the inverter current under dynamic change in the load reactive power.

Fig. 11 : Simulation result of the transient response of adaptive hysteresis current controller (a) grid voltage at VPCC (b) grid current (c) Inverter output phase current and load current (d)Dc-link voltage (e)Reactive power(f)Active power(g) Quadrature component of inverter current

Fig. 12 : Adaptive hysteresis band

As the hysteresis band is function of diaref/dt and VDC hence the band width changes according to the variation of load. by changing the band width the user can control the average switching frequency of the grid connected inverter.

Fig. 13 : Response of reference current, actual current and

current error for hysteresis current controller

The dynamic response of the hysteresis current controller is better than adaptive hysteresis controller but the current error is more in case of hysteresis current controller as shown in fig. 13 as compared to adaptive hysteresis current controller shown in Fig .14.

Fig. 14 : Response of reference current, actual current and

current error for adaptive hysteresis current controller.

Fig. 15 : THD of grid current for hysteresis current controller

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-200

0200

Vol

tage

(V)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

500

Vol

tage

(V)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

5000

P

(W

att)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

5000

Q

(V

ar)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

020

Time(Sec)

Cur

rent

(A)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time(Sec)

Hys

teresis Ban

d

0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-30

-20

-10

0

10

20

30

Time(Sec)

Cur

rent

(A)

Actual CurrentReference CurrentError

0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-30

-20

-10

0

10

20

30

Time(Sec)

Cur

ent(A

)

Refernce currentErrorActual Current

0 500 1000 1500 2000 25000

2

4

6

8

10

Frequency (Hz)

Fundamental (50Hz) = 10.08 , THD= 2.69%

Mag



18

Fig. 16 : THD of grid current for adaptive hysteresis current

controller

Finally, the current harmonic spectrum for Adaptive hysteresis current control method is shown in Fig.16. The THD is 1.72% which is less than THD of hysteresis current controller. THD of hysteresis current controller is 1.79% which is given in Fig.15.

VI. CONCLUSIONS

This paper described the dynamic performance of adaptive hysteresis current controller for grid connected inverter system during load variations. The study includes independent control of active and reactive power of the utility end, harmonic current reduction via current error minimization and lesser THD at the PCC. From the study we observed that, adaptive hysteresis current controller can enable to reduce the current error at load terminal, thus in turn it reduces the THD of load current and it provides nearly constant switching frequency of operation by adjusting its hysteresis-band. In addition, we also observed that the voltage profile at PCC can be maintained constant irrespective of the variation of the reactive power consumption and it reduces the EMI effects, which are the important requirements of the distribution system to satisfy the sensitive loads like medical equipments etc.

REFERENCES

[1] Chai Chompoo-inwai; Wei-Jen Lee; Fuangfoo, P.; Williams, M.; Liao, J.R.;“System Impact Study for the Interconnection of Wind Generation and Utility System” , IEEE Trans. on Industrial Applications Volu: 41 , no.1 ,, Pp.163 – 168, 2005.

[2] F.Blaabjerg, Zhe Chen, and S.B. Kjaer. “Power Electronics as Efficient Interface in Dispersed Power Generation Systems”, IEEE Transactions on Power Electronics, 19(5):1184–1194, Sept. 2004.

[3] Blaabjerg, F.; Teodorescu, R.; Liserre, M.; Timbus, A.V., “Overview of Control and Grid Synchronization for Distributed Power Generation Systems” IEEE Transactions on Industrial Electronics, Vol.:53, Issue:5, Page(s): 1398 – 1409, 2006

[4] Rahman, M.A.; Radwan, T.S.; Osheiba, A.M.; Lashine, A.E.; “Analysis of Current Controllers for Voltage-Source Inverter” IEEE Trans. on Industrial Electronics, Vol: 44 , no. 4, Pp. 477 – 485, 1997

[5] M.P.Kazmierkowaski, L.Malesani: “PWM Current Control Techniques of voltage source converters-A Survey” IEEE. Trans. On Industrial Electronics,.Vol.45, no.5, pp.691-703, Oct.1998

[6] D.M. Brod and D.W. Novotny: “current control of VSI-PWM inverter”, IEEE Trans. Industrial Applications., Vol. IA,. pp.562-570, May/June 1985

[7] Bhim Singh, Ambrish Chandra, Kamal Al-Haddad, Anuradha, D. P. Kothari,” Reactive power compensation and load balancing in electrical power distribution system” International Journal of Electrical Power & Energy Systems, Volume 20, Issue 6, Pp:375-381, August 1998..

[8] Davari M,Salabeigi I.; Gharehpetian G.B, Fathi, S.H. Milimonfared J.”Multifunction Current Controller for Inverter-Based Distributed Generation using Combined PI-Sliding Mode Controller via Sigma-Delta Modulation ” IEEE Inter. Sym. On Industrial Electronics, 2009, ISIE, Page(s): 1803 – 1808, 2009

[9] Ho, C.N.-M.,Cheung, V.S.P.,Chung, H.S.-H.” Constant-Frequency Hysteresis Current Control of Grid-Connected VSI without Bandwidth Control”,IEEE Trans. on Power Electronics, TPEL?2009Volume: 24, no. 11 ,Pp:2484 – 2495, 2009.

[10] Ghani, P.; Chiane, A.A.; Kojabadi, H.M.; “An adaptive hysteresis band current controller for inverter base DG with reactive power compensate” Proc. of IEEE, Pp. 429 –434.,009.

[11] B.K. Bose, An adaptive hysteresis band current control technique of a voltage feed PWM inverter for machine drive system, IEEE Trans. Ind. Electron. 37 (5) (1990) 402–406.

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reactive power compensation in inverter interfaced...

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