［ Control of Power Demand & Supply and Grid Power System ］

Demonstrative Research Projectto Stabilize Output of Hybrid PV
Power Generation Systems(PV ＋ MH ＋ Capacitors)
Keywords

Yoshinobu Ueda,Shunji Oyabu

Photovoltaic (PV) power generation, Micro-hydropower generation, Electric double layer capacitor, Output stabilization

Abstract

As an energy source that is eco-friendly, many Photovoltaic (PV) power generation systems are being adopted. Recently, New Energy and Industrial
Technology Development Organization (NEDO) carried out the “Demonstrative
Research Project to Stabilize Output of Hybrid PV Power Generation Systems(PV ＋ MH ＋ Capacitors)” in cooperation with the countries that have areas where
the sunlight and the amount of water ﬂow in rivers change greatly between rainyand dry seasons. As a member of this project, the company developed and manufactured major equipment and facilities for this demonstrative research.
In this project, we developed the “control techniques to relieve output variations in PV generation to minimize adverse inﬂuence upon power quality” withthe use of electric double layer capacitors.

1 Preface
Recently, the amount of Photovoltaic (PV) power
generation systems has been increasing as ecofriendly an energy resource. In supporting thepower in the areas where electricity access is still
limited, construction of small-scale local microgrid
is expected to increase. In such a case, the PV
power system and Micro-Hydropower (Micro-Hydroor MH) are the most suitable technologies to use
because it does not require the installation of any
large-scale power transmission line or supply bases
for fossil fuels.
The hybrid system that comes in combination
with PV power and Micro-Hydro is considered toprovide advantages such that power outputs can becompensated by each other sources in areas wheresunlight and river water volume change greatly
between rainy and dry seasons. This is because theamount of water in the river increases in rainy season when the PV output decreases as a result ofdecrease in sunlight and it is possible to increase
the Micro-Hydro output. On the contrary, in dry season when river water decreases, sunlight increases
and the PV power output becomes high.
However, there is a challenge: PV power issubject to changes in output caused by change inthe sunlight volume, and output control by MicroHydro results in slow follow-up to variation in power
demand. In order to solve this technical problem,
New Energy and Industrial Technology Development Organization (NEDO) started in Fiscal 2007
International Cooperative Demonstration Project
Utilizing PV Power Generation Systems by the nameof “Demonstrative Research Project to Stabilize
Output of Hybrid PV Power Generation Systems”
in cooperation with the Government of the LaoPeopleʼs Democratic Republic. In this project, after
building the facilities, from April to September 2010
a series of veriﬁcation tests was carried out. (Maincontractor of Contract Research: The Okinawa ElectricPower Company, Incorporated / Sub-contractor:
Okinawa Enetech Co., Inc. and Meidensha Corporation) (1)(2)(3) As a member of this demonstrative
research project, we developed various systems
needed for this research project and performed veriﬁcation tests.
This paper introduces the results of veriﬁcation
tests on multiple control methods applying Electric
Double Layer Capacitors (EDLC) for alleviating frequency deviations. The output characteristics ofEDLC observed during a long-time operation arealso introduced.

MEIDEN REVIEW Series No.162 2014 No.327

2 Demonstration System and EDLC
Control

Villagereceiving power

Fig. 1 shows conﬁguration of the system developed for this demonstrative research. We had beenin charge of production of equipment indicated in
22kV distribution line
the dashed-line box. The Micro-Hydro of 110kW,
Scope of ourWeather observation
manufacturing
400V, and 50Hz functions as the main power supply
equipment
Transformer(voltage source) that is interconnected with a 40kW
140kVA
400V/22kV
Distribution
boardPV. The generated power is stepped up to 22kV bya transformer and distributed to various areas
ResistorPCS～
through the transmission lines with the total length
G75kW in total－ for PV
MHof approximately 20km. The DC circuit of PV PowerDC power
110kW
supply－Conditioning Subsystem (PCS) units is connected－with the EDLC (capacity: ±40kW × 30 seconds)
through the DC/DC converter in order to relieve freStation
load
EDLC
quency deviations. There is a load resistor that can±40kW－30s
Measurement
consume a maximum of 75kW, adjustable in 5kW
datasteps. In addition, there is weather observation
Datalogger
equipment to collect meteorological data and thePV40kWdata logger to record data of veriﬁcation testing.
Fig. 2 shows the control block of EDLC applied
Fig. 1 System Configuration
to this system. As the measures taken to relieve freIllustrates the conﬁguration of the system to be developed for thequency deviations, there are three control methods
demonstrative project.
available: ΔP control that regulates the PV output
variation below the preset changing rate,
Δf control that generates active power
Predicted
composite Changing Goal
rate limiter composite
output in order to cancel frequency
output
EDLC＋ value＋＋ output ＋ － output
PV power
deviations, and ΔP ＋Δf control that isgenerationcommand＋＋＋－value
a combination of the above two.
－1Z
SOC control
The State of Charge (SOC) conOutput for SOC
trol was also performed. This control
regulation
Goalvalue
method is used to regulate the state ofEDLC
SOC
EDLC charge toward the goal level
SOC
within the range where the frequency
Dead bandis never inﬂuenced.

3 Result of Evaluation Test
3.1 Comparison of Frequency
Deviation Compensation Response
Characteristics by EDLC Control

Frequency

Fig. 2Changing Change
rate limiter level limiter Goalfrequency ＋－EDLC Control Block

There are three control methods available: ΔP control that regulates the PV output

Fig. 3 shows changes in EDLC
variation below the preset changing rate, the combined control of Δf that generates
active power output in order to cancel frequency deviations, and SOC control of EDLC.
and Micro-Hydro outputs and frequency with time when the DC incoming
Molded Case Circuit-Breaker (MCCB) from PV array
control. In regard to the control constant (outputto PCS was artiﬁcially switched off at time 0 in orderchanging rate) of EDLC, the optimal values indicatedto cause a sudden reduction of PV output having ain Reference (2) are adopted (0.7kW/s for ΔP concapacity of approximately 30kW. Fig. 3 (a) shows
trol and 1.0kW/s for ΔP ＋Δf control). The data used
the EDLC output obtained under ΔP control, andin this case are the 0.1s mean values calculated
Fig. 3 (b) shows the EDLC output under ΔP ＋Δf
from instantaneous values of voltage and current

28MEIDEN REVIEW Series No.162 2014 No.3

30.020.0EDLCPV100EDLC10PV10.0Time (h)Power (kW)40.00.0(a) ΔP control

10.10.01

30.0
20.00.001

EDLC

EDLC－4 ～0 －－3 ～ 40
5 －－3 ～ 35
0 －－2 ～ 30
5 －－2 ～－25
0－1 ～－20
5～ 1－1 － 50～ 10－5 －5～
0～05～ 510 10～
15 15～
20 20～
25 25～
30 30～
35 35～
440 0～

Power (kW)40.0 PV

PV

10.0
0.0

Power (kW)(b) ΔP ＋Δf control(a) Stay time classified by outputs (June 2010)

ΔP

70.0
60.0

10050.0

ΔP ＋Δf(biased: －14.5kW)

40.0

10Time (h)Power (kW)80.030.0(c) MH output

10.01

50.0

ΔP ＋Δf49.6
49.2
48.8
－100.001～90 9095 ～9510 ～10～ 00
10 15～ 05
11 10～ 10
11 1
5 15
12 ～10 20
12 ～15 25
13 ～10 30
13 ～15 35
14 ～10～ 40
14 1
5 45
15 ～10 50
15 ～15～ 55
1616 00～

Frequency (Hz)

0.1
50.4

ΔP
0

102030

40

5060

70

80

Time (s)Voltage (V)(b) Stay time classified by EDLC voltages (June 2010)(d) Frequency

Fig. 3

EDLC and Micro-Hydro Output and Frequency
Deviation Waveforms upon Sudden Decrease inPV Output

Changes in EDLC and MH outputs and frequency with time areshown, observed when a sudden reduction of PV output is artiﬁcially caused under ΔP control and ΔP ＋Δf control.

recorded by 0.1ms sampling.
When the behavior of EDLC output is compared, there is a linear decrease in output under ΔP
control while the gradient of decrement slowly
becomes moderate as the output decreases under
ΔP ＋Δf control. As a result, as shown in Fig. 3 (c),an increase in MH load becomes somewhat greater
under ΔP control and reduction of frequency also
becomes greater (Fig. 3 (d)). While the EDLC output is being reduced, the frequency is almost kept
constant. Under ΔP ＋Δf control, on the other hand,recovery of frequency begins somewhat earlier. In
addition, ﬁne frequency deviation is also suppressed.
In order to relieve frequency deviation attributable to load changes, it can be said that the use ofΔP ＋Δf control is most effective although theamount of energy needed for the EDLC becomessomewhat larger. If the Δf control only is used, therecan be a subject to remain such that responses

Fig. 4

Distribution of Stay Time Classified by EDLC
Outputs and Voltages

Distribution of stay time is shown, classiﬁed by EDLC outputs
and voltages. Diagram (a) shows distribution classiﬁed by outputs and Diagram (b) shows distribution classiﬁed by voltages.

tend to be somewhat delayed at a stage where thefrequency begins to lower shortly after the occurrence of variations in PV output.

3.2 EDLC Output Characteristics aftera Long Time of Operation
In order to grasp the EDLC output characteristics after a long time of operation, we evaluated thestay time for each span of EDLC output and voltage.
Meanwhile, during the period of artiﬁcial PV ON-OFF
actions performed by the project research members
dispatched to the project site, the EDLC has tended
to work against variations far greater than actual PV
output variations. In this paper, we cover one monthin June 2010 when there was no artiﬁcial output
operation. ΔP control was adopted for the EDLC
control system.
Fig. 4 (a) shows the stay time of the respective output modes. In June 2010, the operation ofMEIDEN REVIEW Series No.162 2014 No.329

charge-discharge was carried out within the rangeof 30kW at the maximum against natural PV output
variations. At that time, nearly 90% of output conditions were kept within 5kW of charge-discharge.
The result was the same in August 2010 when noartiﬁcial testing was carried out by project researchmembers.
Fig. 4 (b) shows the stay time of the EDLC
voltage levels. Since the EDLC characteristicallytries to maintain 133V if there is no variation in PVoutput, the stay rate of 130 ～ 135V occupies morethan 98% of all. The voltage distribution is kept within the range of 105 ～ 155V and this implies thatapproximately 75% of energy was used within therange of 90 ～ 160V where the EDLC can maintainits operation.
Although both output and voltage have somemargins in regard to their design values, there canbe some possibility of no occurrence of the mostrigorous condition because the evaluation period isshort. In addition, reduction of EDLC capacity isalso anticipated due to aged deterioration. Given
the aforementioned, the design for this project isconsidered largely appropriate.

4 Postscript
In the Lao Peopleʼs Democratic Republic, weconstructed the stand-alone hybrid power supply
demonstrative facilities using PV, Micro-Hydro, andEDLC. For the major purpose of relieving frequency
deviations, we made data acquisition and compari-30

MEIDEN REVIEW Series No.162 2014 No.3

son from the demonstration test by multiple EDLC
control methods. For system management after thecompletion of demonstration test, we decided touse the method of ΔP ＋Δf control because thistype of control can provide well balanced reactions
to PV output variations and load changes. As aresult of EDLC output characteristics, we conﬁrmedthat our facility design for this demonstrative research
was fairly appropriate.
We expect that by the result of this demonstrative research, it will become one of the eco-friendly
power supply systems contributing to solving the noelectricity access areas.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.
《References》( 1 ) Ueda et al: “Preliminary Report on the Result of the Project Site
Commissioning Test – Hybrid Power Supply Project of PV, MicroHydro, EDLC in Laos,” 2010 Meeting of Electric Power and Energy
Society, The Institute of Electrical Engineers of Japan, No.231,
pp.26-11〜26-12, 2010. 9 (in Japanese)( 2 ) Ueda et al: “Demonstrative Test on the Hybrid Power Supply
Project in the Lao Peopleʼs Democratic Republic,” Joint Technical
Meeting Panel on Electric and Electric System Technologies andSemiconductor Power Converters, PE-11-002/PSE-11-019/SPC-11056, 2011.3 (in Japanese)( 3 ) Ueda et al: “Demonstrative Test on the Hybrid Power Supply
Project in the Lao Peopleʼs Democratic Republic – Comparison ofthe Effect of Frequency Deviation Suppression by Capacitor ControlSystem –,” 2011 Meeting of Applied Industries Society, The Instituteof Electrical Engineers of Japan, No.1-11, pp.I-133〜I-134, 2011.9 (inJapanese)