1762 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 26, NO. 3, AUGUST 2011
Loading Balance of Distribution Feeders
With Loop Power Controllers Considering
Photovoltaic Generation
Chao-Shun Chen, Senior Member, IEEE, Cheng-Ta Tsai, Chia-Hung Lin, Member, IEEE, Wei-Lin Hsieh, and
Te-Tien Ku
Abstract—For the operation of distribution systems, loading
balance of distribution feeders is important for reducing power
loss and mitigating power flow overloading. In this paper, a loop
power controller (LPC) is applied for the control of real power
and reactive power flows by adjusting voltage ratio and phase
shift so that the loading balance of distribution feeders can be
obtained. To incorporate photovoltaic (PV) power generation in
feeder loading balance, a Taipower distribution feeder with large
PV installation is selected for computer simulation. Daily loading
unbalance is determined by analyzing PV power generation
recorded by the SCADA system and by constructing daily power
load profiles based on distribution automation system (DAS) data.
The load transfer required to achieve loading balance and the line
impedance of distribution feeders are used to derive the voltage
ratio and phase shift of the LPC. Computer simulations indicated
that loading balance can be achieved in distribution feeders with
large PV system installation by using loop power controllers
according to the variation of solar energy and power loading of
study feeders. The system power loss reduction resulting from
feeder loading balance by LPC is also investigated in this paper.
Index Terms— Distribution automation system, loop power
con-troller, photovoltaic.
I. I
NTRODUCTIONR
ENEWABLE energy resources such as wind and solar
en-ergy are increasingly integrated in power system
plan-ning and operation to achieve
emission reductions and
to reduce consumption of fossil fuels by conventional thermal
power generation. Penetration of wind power generation and
PV power generation into distribution systems is expected to
increase dramatically, which raises concerns about system
im-pact by the intermittent power generation of DG [1]–[3].
Com-pared to large-scale wind power and conventional bulk
gener-ation, the generation cost of a PV system is relatively higher.
Manuscript received August 01, 2010; revised October 17, 2010; accepted December 16, 2010. Date of publication January 28, 2011; date of current ver-sion July 22, 2011. This work was supported in part by the National Science Council, Republic of China under the Contract NSC98-3114-E-214-001. Paper no. TPWRS-00622-2010.
C.-S. Chen is with the Department of Electrical Engineering, I-Shou Univer-sity, Ta-Hsu Hsiang, Kaohsiung County, Taiwan, and also with the Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan. C.-T. Tsai and T.-T. Ku are with the Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan.
C.-H. Lin and W.-L. Hsieh are with the Department of Electrical Engi-neering, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan (e-mail: [email protected]).
Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TPWRS.2010.2102052
However, many countries offer significant financial subsidies to
encourage customers to install PV systems. To achieve the goal
of 1000 MW PV installed capacity by 2025, the Taiwan
gov-ernment has launched a promotion program to subsidize 50%
of the PV installation cost and has increased the selling price of
PV generation to 40¢/kWh [4].
It is critical for distribution systems to achieve loading
balance of main transformers and feeders to prevent the system
overloading problem during the summer peak period due to the
usage of air conditioners. Loading balance is also important
for both schedule outages and service restoration after fault
isolation to perform load transfer between distribution feeders.
To achieve better distribution system planning, loading balance
is designed by the optimal reconfiguration of distribution
networks so that system load demand can be evenly allocated
among feeders and main transformers in substations. For
distribution system operation, the loading balance is obtained
by changing the open/closed status of line switches along
distribution feeders so that partial loading of heavily loaded
feeders/transformers can be transferred to relatively lightly
loaded feeders/transformers with the adjustment of service
zones.
However, feeder loading varies from time to time, which will
make it very difficult to obtain the desired load balance with
the network configuration in the system planning stage.
Fur-ther, with more and more renewable distributed generation such
as wind power and PV power being installed in distribution
feeders, loading balance of distribution systems becomes more
of a challenge due to the injection of intermittent power
gen-eration. Applying power electronics based flexible AC
trans-mission system (FACTS) has been proven highly effective for
controlling the load transfer between feeders to achieve loading
balance [5].
Considerable efforts have been proposed in the previous
works to solve the loading balance of distribution systems. The
distribution static compensator (DSTATCOM) was considered
for compensation of loading unbalance caused by stochastic
load demand in distribution systems [6]. The control algorithm
for static var compensation (SVC) has been developed for
loading balance at any given power factor [7]. Fuzzy
multiob-jective and Tabu search have been used to optimize the on/off
patterns of tie switches and sectionalizing switches to achieve
feeder loading balance in distribution systems with distributed
generators [8]. A heuristic-expert system approach for network
reconfiguration to enhance current balance among distribution
feeders was presented by Reddy and Sydulu [9]. A Petri-Net
CHEN et al.: LOADING BALANCE OF DISTRIBUTION FEEDERS WITH LOOP POWER CONTROLLERS 1767
Fig. 13. Voltage ratio and phase shift with the control of LPC (with PV system).
Fig. 14. Loading balance of both feeders with the control of LPC (with PV system).
Fig. 15. Percentage of system power loss before and after applying LPC for loading balance (with PV system).
the peak load period. The power loss over the daily period is
re-duced from 3457 kWh (2.8%) to 2970 kWh (2.3%) after loading
balance by LPC. The system power loss reduction has therefore
been obtained after implementing the LPC for loading balance.
V. C
ONCLUSIONSThis study evaluates a power electronics-based loop power
controller to replace the open-tie switch for the control of real
power and reactive power transfer between distribution feeders
to achieve loading balance of distribution system. The voltage
ratio and phase shift adjusted by LPC are derived according
to mismatches of real power and reactive power loadings
be-tween test feeders for each study hour. To demonstrate the
ef-fectiveness of LPC for the enhancement of loading balance, a
Taipower distribution system consisting of two feeders with a
large-scale PV system has been selected for computer
simula-tion. The power loadings of the study feeders and the PV power
generation have been recorded. By applying the control
algo-rithm of LPC to adjust the voltage ratio and phase shift
be-tween both feeders, the proper amount of real power and
reac-tive power can be transferred from the heavily loading feeder to
the lightly loading feeder for each study hour. According to the
computer simulation, it is concluded that the loading balance of
distribution systems with intermittent PV power generation can
be obtained effectively by the implementation of LPC to achieve
adaptive control of load transfer between distribution feeders.
The power loss reduction of test feeders after loading balance
by LPC has also been derived in this paper.
R
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Chao-Shun Chen (M’84–SM’06) received the B.S. degree from National
Taiwan University, Taipei, Taiwan, in 1976 and the M.S. and Ph.D. degrees in electrical engineering from the University of Texas at Arlington in 1981 and 1984, respectively.
From 1984 to 1994, he was a Professor in the Electrical Engineering De-partment at National Sun Yat-Sen University, Kaohsiung, Taiwan. From 1989 to 1990, he was with Empros Systems International. Since October 1994, he has worked as the Deputy Director General of the Department of Kaohsiung Mass Rapid Transit. From February 1997 to July 1998, he was with the Na-tional Taiwan University of Science and Technology as a Professor. From Au-gust 1998 to January 2008, he was with the National Sun Yat-Sen University as a Professor. Since February 2008, he has been with I-Shou University as a Chair Professor and with National Sun Yat-Sen University as a Joint Professor. His majors are computer control of power systems as well as electrical and me-chanical system integration of mass rapid transit systems.
Cheng-Ta Tsai received the M.S. degree in electrical engineering from National
Sun Yat-Sen University, Kaohsiung, Taiwan, in 2004. He is currently pursuing the Ph.D. degree in electrical engineering of National Sun Yat-Sen University.
Chia-Hung Lin (S’95–M’98) received the B.S. degree from the National
Taiwan Institute of Technology, Taipei, Taiwan, in 1991, the M.S. degree from the University of Pittsburgh, Pittsburgh, PA, in 1993, and the Ph.D. degree in electrical engineering from the University of Texas at Arlington in 1997.
He is presently a full Professor at the National Kaohsiung University of Ap-plied Sciences, Kaohsiung, Taiwan. His area of interest is distribution automa-tion and computer applicaautoma-tions to power systems.
Wei-Lin Hsieh received the M.S. degree in electrical engineering from I-Shou
University, Kaohsiung, Taiwan, in 2009. He is currently pursuing the Ph.D. degree in electrical engineering of National Kaohsiung University of Applied Sciences.
Te-Tien Ku received the M.S. degree in electrical engineering from National
Sun Yat-Sen University, Kaohsiung, Taiwan, in 2005. He is currently pursuing the Ph.D. degree in electrical engineering of National Sun Yat-Sen University.
