IEEE Electrification Magazine - June 2017 - 35

Subsystem 1|CTLs|Vars
50.1

Subsystem 1|CTLs|Vars

Frequency

50.1

50.05

49.95
7 kV

49.95
6.4 kV

Versus
Vs

6.2

6.5

6
5.5
0

Frequency

5.8
10

30
Seconds

5.6
0

(a)

30
Seconds

(b)

Figure 8. Frequency and voltage curves in two configuration modes (a) and (b) when the load changes suddenly: (a) PV-diesel mode 2 and
(b) PV-diesel-storage mode 2.

power balance and keep the voltage stable. The voltage
fluctuations in PV-diesel-storage mode 1 and PV-diesel
mode 1 are large and exceed the allowable range of ±5%.
The voltage fluctuation in PV-diesel mode 1 reaches ±10%,
because there is no energy storage in this mode.

capacity configuration must be studied through detailed economic and reliability evaluations. This article presents the
methodology and process for this study, which will help to
optimize the economy of a large-scale microgrid and ensure
the stable operation of the microgrid at the same time.

Sudden Large Load Change

For Further Reading

The simulations of sudden large load change are done for
PV-diesel-storage mode 2 and PV-diesel mode 2, in which
the voltage fluctuations are within the allowable range of
±5% in a sudden large light intensity change test. Consider
the following scenario: after the system reaches the steady
state, there is a sudden 1-MW load increase (change from
9.5 to 10.5 MW) at 15 s, and there is a sudden 1-MW load
decrease (return to 9.5 MW) at 25 s. The frequency and
voltage curves in these two modes are shown in Figure 8.
The frequency fluctuations in the two configuration modes
are very small (within the allowable range of ±0.2 Hz). The
voltage fluctuation in PV-diesel mode 2 exceeds the allowable range of ±5%. The voltage fluctuation in PV-diesel-storage mode 2 is within the allowable range of ±5%, because
when the load changes suddenly, both the rapid responding diesel generators and the energy storage devices will
help to maintain the system power balance and keep the
voltage stable. The simulation results in these two scenarios show that, from the perspective of reliability, the ranking (from the best to the worst) of the four configuration
modes is as follows: PV-diesel-storage mode 2, PV-diesel
mode 2, PV-diesel-storage mode 1, and PV-diesel mode 1.

Conclusions
The analysis and simulation results show that the configuration mode with the best economic benefit has the lowest
reliability. The economic benefit and the reliability of the
microgrid are normally conflicted in reality. Therefore, to
achieve the highest benefits from a microgrid, an appropriate

J. Xiao, L. Bai, and F. Li. "Sizing of energy storage and diesel
generators in an isolated microgrid using discrete Fourier
transform (DFT) [J]," IEEE Trans. Sustainable Energy, vol. 5, no. 3,
pp. 907-916, 2014.
M. Kermani, "Transient voltage and frequency stability of an
isolated microgrid based on energy storage systems [C]," in Proc.
IEEE 16th Int. Conf. Environment and Electrical Engineering,
Florence, Italy, 2016, pp. 1-5.
Z. Peng, L. Haitao, and Z. Minglu, "Research overview of optimization of multi-source and energy storage in microgrid [C]," in
Proc. 12th IET Int. Conf. on AC and DC Power Transmission, Beijing,
China, 2016, pp. 1-5.
S. Sharma, S. Bhattacharjee, and A. Bhattacharya, "Grey
wolf optimization for optimal sizing of battery energy storage
device to minimize operation cost of microgrid [J]," IET Generation, Transmission Distribut., vol. 10, no. 3, pp. 625-637, 2016.
S. N. G. Dhanis Woro Fittrin, F. Danang Wijaya, and S Pramono
Hadi, "Optimal configuration of PV-Wind turbine-grid-battery in
low potency energy resources," in Proc. 6th Int. Conf. Information
Technology and Electrical Engineering (ICITEE), 2014, pp. 1-6.

biographies
Hu Xie (xiehu@sgepri.sgcc.com.cn) is with the NARI Technology Co., Ltd., State Key Lab of Smart Grid Protection
and Control.
Shu Zheng (zhengshu@sgepri.sgcc.com.cn) is with the
NARI Technology Co., Ltd., State Key Lab of Smart Grid
Protection and Control.
Ming Ni (ni-ming@sgepri.sgcc.com.cn) is with the NARI
Technology Co., Ltd., State Key Lab of Smart Grid Protection and Control.

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