IEEE Electrification - December 2020 - 65

Typical Day 2: Low PV Outputs

Typical Day 3: Obvious Fluctuation in the PV Output
The typical day 3 operating curve is shown in Figure 15.
There is a peak in the load curve from 8:00 p.m. to 10:00 p.m..
The output curve of the PV system is relatively low and
has obvious fluctuations at 1:00 p.m. The energy-storage
system is charged during the valley period of the electricity price and discharged during the peak period during the day. It is worth noting that, when the PV
output suddenly changes, the EMS can adjust the
operation state of the system in a timely manner,
increase the purchase of electric energy, and store it.
This can not only reduce the power consumption during the period of high electricity price but also reduce
the maximum value of the transmission line power
flow as much as possible.

400

300

300

PV Output (kW)

400

200

100

0

Load (kW)

price difference between the load peak and load valley. On
typical day 2, the purchased power is reduced by 24.5%
(from 57,337 to 43,280 kWh), and the corresponding power
purchase cost is reduced by 34.02% (from ¥32,364 to
¥21,353).

0

2

4

6

200

100
0

8 10 12 14 16 18 20 22 24
Time
(a)

1,200

1,200

1,000

1,000
Load (kW)

PV Output (kW)

The operation curve of typical day 2 is shown in Figure 14.
The load demand of the microgrid has two peaks, which
appear at 1:00 a.m. and 8:30 p.m., respectively, and the
output of the PV is always less than the load demand.
Therefore, in the case in which the electricity generated by
PV is completely used by the microgrid itself, it is necessary to purchase electricity from the external power grid
to meet the power demand. To reduce the electricity purchased by the microgrid when the electricity price is high,
the energy-storage system is charged from 2:00 a.m. to
7:00 a.m. and discharged from 9:00 a.m. to 11:00 a.m. and
8:00 p.m. to 10:00 p.m. However, the smaller PV output
makes the energy-storage system unable to charge from
1:00 p.m. to 3:00 p.m., which makes the power on the tie
line decrease less during the peak load at night. There is
no more stored power to reduce the purchased power in
the next day from 12:00 a.m. to 3:00 a.m., so the capacity
does not decrease.
Due to the low PV output, the microgrid cannot reduce
the capacity tariff, but it can still make a profit from the

800
600
400
200

0

24

48

72
Time
(b)

96

120

144

168

0

24

48

72
Time
(d)

96

120

144

168

800
600
400
200

0

2

4

6

0

8 10 12 14 16 18 20 22 24
Time
(c)
Actual Value

Predicted Value

Figure 12. The results of power load forecasting and PV output forecasting for the Xi'an Industrial Park microgrid: (a) daily and (b) weekly PV output as well as (c) daily and (d) weekly load.

	

IEEE Elec trific ation Magazine / D EC EM BE R 2 0 2 0

65



IEEE Electrification - December 2020

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