impact of distributed generation on system stability using ... · load flow solutions according to...

119 Shraddha Sureshkumar Dhoot, Ravishankar Kankale

International Journal of Electronics, Electrical and Computational System

IJEECS

ISSN 2348-117X

Volume 6, Issue 1

January 2017

Impact of Distributed Generation on System Stability using PV

Curve

Shraddha Sureshkumar Dhoot Ravishankar Kankale

ME (EPS)- Student Assistant Professor

SSGMCE, Shegaon SSGMCE, Shegaon

SGBAU SGBAU

Abstract – There has been growing concern in

distribution system regarding impacts of distributed

generation (DG) specifically on voltage stability. The key

purpose of this paper is to estimate the voltage stability

of power systems with increased level of distributed

generation resources based on PV curve. In this

technique, the stability of power systems is evaluated

with increased penetration level of distributed generation

resources. The ultimate objective of this paper is

studying the impacts of DG units under diverse

Penetration level on few problems such as voltage

stability, voltage profile, power flow and PV curve for

each bus. In this paper IEEE 14 bus system is simulated

in PSCAD and load flow is done in MATLAB

Index Terms - distributed generation(DG),voltage

stability, PV curve, penetration level.

I. INTRODUCTION

In the recent past, one of the problems that received

wide attention among utilities is the voltage

instability [2]. The integration of distributed

generation (DG) to power system networks has

quickly increased from renewable- energy sources.

This increase can be clarified by elements such as

environmental concerns, the growth of electricity

businesses, the advance of technologies, goals

related to emission reduction, energy independence,

improved infrastructure reliability and so on [3].

The voltage stability of a DG integrated grid

usually depends on the capacity, the control

strategies and the interconnected locations of the

DGs [5]. DG units have a small size compared to

central power plants so the impact is slight if the

penetration level is low (1%- 5%). If the

penetration level of DG is increased to 20%-30% of

the level, the impact of DG units will be deep [8].

The energy structure of the grid will change if DG

penetration increases it affects the grid voltage,

power quality and the operational planning [3],

among which voltage stability problem is an

important aspect. The voltage stability is concerned

with the capability of a power system to sustain

suitable voltages at all nodes in the system under

normal condition and after being subject to a

disturbance. Careful engineering can eliminate

these adverse impacts that DG penetration could

impress on the electric delivery system [4]. We say

power system has a state of voltage instability when

a disturbance causes a progressive and un-

controllable decrease in voltage level. The size, the

technology and the placement of DG play an

important role in the operation of distribution

systems. For long-term voltage stability analysis,

bus-based voltage indices are implemented using

Power-Voltage curves (PV curves) to analyze the

contribution of DG.

II. VOLTAGE STABILITY

Fig. 1 shows a typical PV curve. Voltage stability

problems mainly occur when the system is heavily

stressed beyond its capability. While the

disturbance leading to voltage collapse may be

initiated by a variety of causes, the main problem is

the inherent weakness in the power system. Mostly,

the P-V curves are used in order to forecast the

voltage security. P-V curves are most considerable

method to find active power margin and are used to

determine the loading margin of a power system.

The load of power system is gradually increased

and at each increment it is necessary to recomputed

power flows until the nose of the PV curve is

reached [6].



IJEECS

ISSN 2348-117X

Volume 6, Issue 1

January 2017

Fig. 1 PV Curve

They are obtained by applying a continuous

power flow method [6]. The critical point Pmax in

the P-V curve represents the maximum loading of a

system. The stability margin is defined as the MW

distant from the operating point to the critical point.

The penetration of the DG units in a distributed

system may increase or decrease the voltage

stability margin subject on their operation at unity,

lead or lag power factors [3].

III. SELECTION OF THE CANDIDATE BUSES

The buses for DG installation can be selected by

calculating voltage stability indices. The base

which has the lowest voltage (sensitive base to the

voltage stability) is selected as candidate bus. Since

this study is focusing on improving the voltage

stability of the system, it uses voltage sensitivity

analysis to select the buses. Additionally, it should

be located in the main feeders of the system. The

method is conducted by testing the voltage

sensitivity to the change of the DG injected power.

The DG units are then modelled as PQ buses, since

they are not used to control the system voltage [2].

In this case, it can be used to study the impact of

the DG units on voltage stability, voltage profile,

power flow and P-V curve.

IV. SYSTEM UNDER STUDY

IEEE standard 14 bus system is taken as system

under study, its single line diagram is as shown in

Fig. 2. It consists of 14 buses, 20 branches, 2

generation buses, 3 compensator, 11 load buses,

total generation of 272.4 MW and 78.5 MVAR,

total load of 259MW and 73.5 MVAR.

Fig. 2 Single line diagram of the IEEE 14-bus

system.

V. RESULTS

In this paper first we draw PV curves by simulating

the system in PSCAD 4.2.0. and then again we

draw them using continuation power flow CPF by

using MATLAB Here two cases are considered (a)

without DG (b) with DG.

1. PSCAD RESULTS:

The voltage of bus is monitored by varying the load

connected on the bus for both the cases and PV

curves are drawn for the same. Fig. 3 Simulation of

IEEE 14 bus Test system model during Normal

condition in PSCAD. Following are the PV curves

plotted in PSCAD.

Fig. 3 Simulation of IEEE 14 bus Test system

model during Normal condition in PSCAD



IJEECS

ISSN 2348-117X

Volume 6, Issue 1

January 2017

Fig. 4 PV curve of bus 4 without dg (blue curve)

and with DG of (a)2MW (green curve) and

(b)5MW (red curve


and with DG (a)2MW (green curve) and (b)5MW

(red curve)



(red curve)



(red curve



(red curve)



(red curve)



IJEECS

ISSN 2348-117X

Volume 6, Issue 1

January 2017

Fig.10 PV curves of all 14 buses without DG in

PSCAD

Fig. 11 PV curves of all 14 buses with DG of

2MW connected in PSCAD

Fig. 12 PV curves of all 14 buses with DG of

5MW connected in PSCAD



(red curve)



(red curve)



(red curve)

2. MATLAB RESULTS:

Continuation power flow method is used to plot PV

curve in MATLAB. The general principle behind

the continuation power flow is quite simple. It

works on a predictor-corrector scheme to find a

solution path. It adopts locally parameterized

continuation technique. It comprises load



IJEECS

ISSN 2348-117X

Volume 6, Issue 1

January 2017

parameter, step length for load parameter and state

variable. Continuation power flow finds successive

load flow solutions according to a load scenario.

From a known base solution, a tangent predictor is

used so as to estimate next solution for a specified

pattern of load increase. The corrector step then

governs the exact solution using Newton-Raphson

technique employed by a conventional power flow.

After that a new prediction is made for a definite

increase in load based upon the new tangent vector.

Then corrector step is applied. This process goes

until critical point is extended. The critical point is

the point where the value of tangent vector is zero.

Fig. 16 PV curve of all the 14 bus without DG in

MATLAB using continuation power flow method

Fig. 17 PV curve of all the 14 bus with 50% DG in

MATLAB using continuation power flow method

VI CONCLUSION

This paper work emphases on analysing voltage

stability, voltage profile, power flow and the P-V

curve of a system with integrate DG. From the

above Fig. no 4 to Fig. no 12, it can be clearly seen

that the voltage stability of the buses has been

improved whereas it is decreased for bus 8, 9 and

10 refer fig.13, 14 and 15. The simulation results

designate the maximum penetration level of the

wind turbine units is commended to be placed in

the most sensitive voltage buses in order to improve

the voltage stability margin. As we go on increasing

the DG, loadability increases. So, voltage profile of

the buses may increase or decrease depending upon

the placement, size and technology used. The

technique for continuous load flow has been

applied to determine the PV curves of the 14- node

IEEE test system, and it has been shown that a

4.545% load increment can lead to the instability of

the system, and it also has been determined that the

node 14 is the weakest node of the system.

Table I: Impact of DG on maximum loading point

DG %

Lodability

(predictor)

Lodability

(corrector)

0% 4.05 4.043

10% 4.418 4.408

20% 4.418 4.408

30% 4.507 4.494

40% 4.55 4.537

50% 4.566 4.545

60% 4.545 4.53

70% 4.507 4.492

80% 3.765 3.765

REFERENCES

[1] Jason M. Sexauer and Salman Mohagheghi, ”

Voltage Quality Assessment in a Distribution System

With Distributed Generation—A Probabilistic Load

Flow Approach” IEEE TRANSACTIONS ON

POWER DELIVERY, VOL. 28, NO. 3, JULY 2013.

[2] Arthit Sode-Yome, Nadarajah Mithulananthan, and

Kwang Y. Lee, ” A Maximum Loading Margin

Method for Static Voltage Stability in Power

Systems” IEEE TRANSACTIONS ON POWER

SYSTEMS, VOL. 21, NO. 2, MAY 2006.

[3] Mostafa H. Mostafa, Mostafa A. Elshahed and

Magdy M. Elmarsfawy,” Power Flow Study and

Voltage Stability Analysis for Radial System with

Distributed Generation” International Journal of



IJEECS

ISSN 2348-117X

Volume 6, Issue 1

January 2017

Computer Applications (0975 – 8887) Volume 137 –

No.9, March 2016.

[4] P. Srikanth, O. Rajendra, A. Yesuraj, M. Tilak

K.Raja , “Load Flow Analysis Of Ieee14 Bus System

Using MATLAB” International Journal of

Engineering Research & Technology (IJERT) Vol. 2

Issue 5, May - 2013 ISSN: 2278-0181 .

[5] X. Hu1, X. Zhang1, X. Lou2, X. Meng2, J. Zhang1,

T. Li2 and S. Pan2, “Analysis on the Voltage

Stability and the Allowed Penetration Capacity of

Distributed Generations in Yuhang Power Grid” 9th

International Conference on Power Electronics-

ECCE Asia June 1 - 5, 2015 / 63 Convention Center,

Seoul, Korea.

[6] R. Darbali Zamora , J. M. Arias Rosado, and Dr. A.

J. Díaz Castillo, “Stability Analysis of Wind Energy

Generation in the Electrical System of Puerto Rico”,

International Conference on Renewable Energies

and Power Quality (ICREPQ’14) Cordoba (Spain),

8th to 10th April, 2014 Renewable Energy and

Power Quality Journal (RE&PQJ) ISSN 2172-038

X, No.12, April 2014.

[7] U. Parul Anand1, P.Dharmeshkumar2, “VOLTAGE

STABILITY ASSESSMENT USING

CONTINUATION POWER FLOW”, International

Journal of Advanced Research in Electrical,

Electronics and Instrumentation Engineering (ISO

3297: 2007 Certified Organization)Vol. 2, Issue 8,

August 2013.

[8] P.Kundur: Power: System Stability and Control, New

York: McGraw-Hill, 1994.

[9] 1

Nguyen Tung Linh 2

;Trinh Trong Chuong;,

“VOLTAGE STABILITY ANALYSIS OF GRIDS

CONNECTED WIND GENERATORS”.

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