The document presents a simple algorithm for distribution system load flow analysis that can accommodate distributed generation. It begins by outlining the objectives, motivation and special features of distribution networks that require modified load flow analysis. It then describes the proposed forward-backward sweep method and models for loads and distributed generation. The algorithm is tested on three test systems and results show reductions in losses and improved voltage profiles with distributed generation integrated using the proposed method and models.

1. A Simple Algorithm for Distribution
System Load Flow with Distributed
Generation
Presented by:
Sivkumar Mishra
IIIT Bhubaneswar

2. Objective:
To choose a suitable model of DGs and to perform
power distribution system load flow.
Motivation:
With increasing penetration of DGs in distribution
system, the usual passive power distribution
systems have become active ones. Distribution
system load flow being an important tool for steady
state analysis needs to modified accordingly.

3. Special Features of Power Distribution Networks
• Radial Structure
• High R/X of the feeders
• Multiphase and Unbalanced Operation
• Large No. of Buses

4. Distribution System Load Flow Methods
• High R/X ratios of feeders make the system ill
conditioned for load flow.
• Special load flow methods developed to exploit the
topological characteristics of distribution systems
• Forward Backward Sweep(FBS) is the most popular
DSLF method

5. Forward Backward Sweep Based DSLF
a' a aa aV =V - z .I (1)
Equivalent single phase feeder

6. Modeling of Loads as ECIs
Equivalent Current Injections (ECI)
*
( )/ , 1,2............ (2)Li i i iI P Q V i nb  
Pi and Qi in this case are equal to the corresponding loads PLi and QLi at
bus-i.

7. Current in any branch of a RDN
Li' ' branch= I (3)j
i all subsequent
buses to j
I Current of j th

 
3 5 63 branch= IL +ILI Current of rd
Branch Current Calculation

8. Forward Backward Sweep Method
• Each iteration consists of two steps i.e backward
sweep followed by a forward sweep
• Backward sweep to calculate the branch currents
• Forward sweep is to update bus voltages with the
values of branch currents obtained in the backward
sweep

9. Proposed Bus Identification Scheme
• For identifying adjacent buses of any bus in a radial
distribution network mf, mt and adb arrays are
proposed.
• mf and mt are the two pointer arrays and adb is the
array which stores all the adjacent buses.

10. Pointer and Storage Operation of mf, mt and adb
Arrays

11. Proposed Bus Identification Scheme
• For identifying subsequent buses of any branch in a
radial distribution network mfs, mts, sb and nsb
arrays are proposed.
• mfs and mts are the two pointer arrays and sb is the
array which stores all the subsequent buses to the
braches of a RDN.
• nsb stores the number of subsequent buses to a
branch.

12. Pointer and Storage Operation of mfs, mts and sb Arrays

13. Flow Chart

14. Distributed Generation
• Distributed Generation (DG) is an electric active power
source connected directly to the distribution network or
customer side of the meter [11].
• It encompasses several technologies which can be broadly
categorized as renewable or nonrenewable.
• Renewable DG includes small hydro plants, wind turbines,
photo voltaic cells, fuel cells, geothermal power plants,
biomass power plants, tidal power plants, wave power
plants etc., whereas non renewable category includes
conventional fossil fuel based generators, micro turbines,
CHP plants etc.

15. Integration of DGs
• Integration of DGs into the distribution systems alters the
basic configuration from a passive system to an active one.
• The major technical benefits are [7]:
- Reduced line losses
- Voltage profile improvement
- Reduced emissions of pollutants
- Increased overall energy efficiency
- Enhanced system reliability and security
- Improved power quality
- Relieved T & D congestion

16. Challenges
• Dugan [8] has enlisted fourteen challenges relevant to the
analysis of DG in the distribution systems such as providing
the screening applications, power flow solution,
multiphase analysis, circuit model size, dynamics,
harmonics, determining the value of DG, modeling sub
transmission, assessing distribution reliability, loss analysis,
protective device coordination, transformer connections
etc.
• Suitable model for power flow solution

17. DG Models for DSLF
• Two types of DG models: constant PQ modeled as
negative loads with currents injecting into the node and
PV nodes [14].
• Teng [13] has proposed three types of mathematical
models of DGs for load flow analysis i.e a) constant power
factor model for synchronous generator and power
electronics based DGs b) variable reactive power model
for induction generator based DGs and c) constant voltage
model for large scale controllable DGs.

18. P-Q Modeling of Loads and DGs

19. Reasons for Opting PQ Model of DGs for DSLF
• DGs are normally smaller in size when compared with the
conventional power sources, the constant PQ model is commonly
found to be sufficient for the distribution system load flow analysis
[17].
• DGs typically not permitted to regulate the voltage. Instead, they
regulate power and power factor, hence modeled as negative loads
[8].

20. DSLF with DGs
With DGs modeled as negative loads, the equivalent loads
at bus-i can be expressed as:
PLi and QLi are the constant power loads connected at bus -i
and Pgi and Qgi are the real and reactive powers injected by
the DG connected at bus-i respectively. The ECIs then can be
calculated at all the buses using (2). The backward and
forward sweeps are then followed as per the flow chart
previously mentioned.
i Li giP P P 
i Li giQ Q Q 
(4-a)
(4-b)

21. Result 12 Bus DS
S/S
1 2 3 4 5 6 7 8 9 10 11 12
DG-1
DG-2

22. Result 33 Bus DS

23. Result 69 Bus DS

24. Load Flow Results
12 Bus RDN 33 Bus RDN 69 Bus RDN
without
DG
With DG
without
DG
With DG
without
DG
With DG
No.
of
iter.s
4 3 4 4 4 4
Exec.
Time
(ms)
2 2 3.9 3.9 7.6 7.6
Total
PLoss
(kW)
20.309 11.89 202.65 130.78 224.15 157.9
Total
QLoss
(kVAR)
8.0432 4.72 135.13 89.38 102.15 70.98

25. Some More Results….

26. Some More Results….

27. Some More Results….

28. Conclusions
• A simple algorithm for DSLF has been proposed with
a novel bus identification technique.
• Modeling issues for integrating DGs has been
discussed and PQ modeling of DGs has been chosen
and the load flows have been performed on 3 test
systems

29. References
1) S. Mishra, and D. Das, “Evolution of distribution system load flow methods-a bibliographic
review,” J Inst.Eng. India EE Div, vol. 91, no.3, pp. 42-48, 2010.
2) U. Eminoglu, and M. H. Hocaoglu, “ Distribution systems forward/backward sweep-based
power flow algorithms: a review and comparision study,” Elect. Pow. Comp. and Sys., vol.
37, pp.91-110, 2009.
3) G.Pepermans, J.Driesen, D.Haeseldanckx,R.Belmans, and W. D’haeseleer, “ Distributed
generation: definition, benefits and issues,” Energy Policy, vol. 33, no.6, pp. 787-798,2005.
4) W. El-Khattam, and M.M.A Salama, “ Distributed generation technologies, definitions and
benefits,” Elect. Pow. Sys. Res., vol. 71, pp. 119-128, 2004.
5) P.Dondi, D.Bayoumi, C.Haederli, D.Julian, and M.Suter, “ Network integration of distributed
power generation,” J. Pow. Sourc., vol. 106, no.1-2, pp. 1-9, 2002.
6) J. A. Pecaslopes, N. Hatziargyrious, J. Mutale, P.Djapic, and N.Jenkins, “Integrating
distributed generation into electric power systems: a review of drivers, challenges and
oppurtunities,” Elect. Pow. Sys. Res., vol. 77, pp. 1189-1203, 2007.
7) P.Chiradeja and R.Ramakumar, “An approach to quantify the technical benefits of
distributed generations,” IEEE Trans. Ener. Conv., vol.19, no.4, pp. 764-773,2004.
8) R.C.Dugan, “Challenges in considering distributed generation in the analysis and design of
distribution systems,” Proc. IEEE PES Gen. Meet., pp 1-8, July 2008.
9) S. Mishra, “ A simple algorithm for unbalanced radial distribution system load flow,” Proc.
IEEE TENCON, pp 1-6, Oct. 2008.
10) S Mishra, D.Das, and S.Paul, “ A simple algorithm to implement active power loss allocation
schemes in radial distribution systems,” J. Inst . Eng. India Ser. B, vol. 93, no.3, pp. 223-232,
2012.

30. References
11) T.Ackermann, G. Anderson and L. Soder, “ Distributed Generation: a definition,” Elect. Pow.
Sys. Res., vol. 57, pp. 195-204, 2001.
12) M.F.Akorede, H.Nizam, and E. Pouresmaeil, “ Distributed energy resources and benefits to
the enviorment,” Sustainable Energy Reviews , vol.14, pp. 724-734, 2010.
13) J.H. Teng, “Modeling distributed generations in three phase distribution load flow,” IET
Gen. Trans. Distrib., vol.2, no.3, pp. 330-340, 2008.
14) S.Khusalani, J.K.Solanki, and N.N.Schulz, “ Development of three phase unbalanced power
flow using PV and PQ models for distributed generation and study of the impact of DG
models,” IEEE Trans. Pow. Deliv. , vol.22, no.3, pp. 1019-1025, 2007.
15) H.E.Farag, E.F.El-Saadany, R. El-Shatshat and A. Zidan, “A generalised power flow analysis
for distribution systems with high penetration of distributed generation,” Elect. Pow. Sys.
Res., vol. 81, pp. 1499-1506, 2011.
16) S.M. Moghaddas-Tafreshi, and E. Mashhour, “ Distributed generation modeling for power
flow studies and three phase unbalanced power flow solution for radial distribution
systems considering distributed generation,” Elect. Pow. Sys. Res., vol. 79, pp. 680-686,
2009.
17) U. Eminoglu, T. Gozel and M. H. Hocaoglu, “ DSPFAP: distribution systems power flow
analysis package using MATLAB graphical user interface(GUI),” Comp. Appl. Engg. Edu., vol.
18. no.1, pp. 1-13, 2010.
18) J-H. Choi, and J-C Kim, “ Advanced voltage regulation method at the power distribution
systems interconnected with dispersed storage and generation systems” IEEE Trans. Pow.
Deliv. , vol. 15, no.2, pp. 691-696, 2000.
19) G.B. Jasmon, and L.H.C. Lee, “Distribution network reduction for voltage stability analysis
and load flow calculations,” Elect. Pow. Eng. Syst., vol. 13, no.1, pp. 9-13, 1991.

31. References
20) J.S. Savier and D.Das, “ Impact of network reconfiguration on loss allocation of radial
distribution systems,” IEEE Trans. Pow. Deliv., vol.22, no.4, pp. 2473-2480, 2007.
21) Z. Ghofrani-Jahromi, Z. Mahmoodzadeh, and M. Ehsan, “ Distribution loss allocation for
radial systems including DGs” IEEE Trans. Pow. Deliv. , vol.28, 2013 ( Future Issue).
22) S Mishra, and D.Das, “ A novel active power loss allocation scheme for unbalanced power
radial distribution systems,” Int. Rev. Electr. Eng.,vol.4,no.4,pp.260-267,2008.
23) S Mishra, D.Das, and S.Paul, “ Active loss allocation schemes in radial distribution
systems,” Cogener. Distributed. Gener. J, vol. 25, no.3, pp. 26-43, 2010.