［ Distributed Power Supply ］

Development of New Megasolar PCS
Models and Functions Conforming
to Feed-in-Tariff System in Japan
Keywords

Kazuho Hasegawa,
Naoto Kameda

Photovoltaic generation, PCS, Megasolar, FIT system, Grid connection

Abstract

Four years have passed since the enforcement of the Feed-in-Tariff (FIT)
System in July 2012. The demands for the construction of solar farms have
rapidly increased in Japan. The demands for our Power Conditioning Subsystems(PCSs), SP310 Series, sharply increased due to our adoption of a 750V system
where maximum DC input voltage is 750V, which is ahead of our competitions.
Along with an increase in solar farms, there have been new rules for grid connections requiring new functions such as a Fault Ride Through (FRT) and customer
requests for PCS price reduction due to the gradual lowering of FIT prices. Under
such circumstances, we could maintain an order amount level for photovoltaic
PCS because of our on-going efforts to develop new PCS models and new functions. This photovoltaic generation market is in a time of big changes. In order toincrease orders in the future, we need to improve our products.

1 Preface
It has been four years since the Feed-in-Tariff(FIT) system was enacted on 1 July 2012. Ahead of
our competitors, we developed Power Conditioning
Subsystems (PCS) of 750V class, the SP310-250T.
We adopted the maximum DC input voltage of 750V
as the highest voltage in the low-voltage classdeﬁned in Japan. Our new PCS models have beenfavorably accepted by our customers because ourmodels help reduce the parts of the power distribution equipment and power distribution losses in thesystem building at the solar farm. This compareswith our conventional 600V-class PCS model. As
such, we increase sales signiﬁcantly in synch with asharp expansion of demand for PCS triggered by
the enforcement of the FIT System. In regard toPCS product lineups for our 750V systems, only one
model of the SP310-250T type was available previously. Then, there were some model changes andnewly developed models were added. Currently,
four models are available: SP310-250T-DG, SP310250T-DN, SP310-100T-DG, and SP310-100T-DN.
We continue on to develop new more models.
This paper explains why, despite our strong
photovoltaic (PV) PCS sales, we made changes tothe models and added new models so frequently insuch a short time of about four years after the startof FIT. We will explain according to the each development factors. This paper also introduces somefuture developments.

2 Development of New Models
While orders of PV PCS kept on increasing
based on the FIT Law, we developed the products
described below according to trend analysis on theordered transactions.

2.1 Development of New PCS Models Exclusively for Outdoor Use
In many cases, the PCS for megasolar farmis installed outdoors. Since the SP310-250T ﬁrst
model uses an indoor panel, we had to prepare andaccommodate it in an outdoor panel for outdoor
application. Under the conditions where we canintake outdoor air into the PCS, the outdoor panel
will be of the fan-cooled type. Meantime, there arechallenging issues like a salt hazard areas whereoutdoor air cannot be taken inside or in the cold
where air temperatures are lower than the speciﬁed
operating temperature range for the equipment. In
such cases, we will select an enclosed package ofthe air-conditioned cooling type for the outdoor panel.
While the number of received orders increased, theinstallation condition requiring air-cooled outdoor
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Table 1

Outdoor Installation Type PCS: Specifications ofMaximum Output 250kW and 100kW Models

Speciﬁcations of SP-310-250T-DG and SP-310-100T-DG areshown. Both types are uniﬁed into the 750V system based on theMPPT control voltage range of 400-750V.

DC input

Model(Outdoor installation type)

Outdoor Installation Type PCS, SP-310-250T-DG

400〜750

Ratedvoltage ( V )500

Input circuit

2 circuits

2.2 Development of PCS Models with aMaximum Output of 100kW
Since the SP310-250T speciﬁes the maximum
output of 250kW, the PCS capacity for the megasolar
farm comes in 250kW or its multiples. The solar panel
installation capacity is dependent in many cases on
the site area where the panels can be installed. ThePCS capacity therefore, often required to be lessthan 250kW or its multiples. In responding to thissubject, we developed a PCS model with a maximum output of 100kW (“100kW unit” hereafter) by
the name of the SP310-100T Series. We alreadyhad a 100kW model in the past (see SUNGENEC
Series: Meiden Jiho No.324, 2009/No.3, pp.64-69.).
The main reason why we developed a new 100kW
unit in this time is that the 100kW model adopts theDC 750V system. This is a key feature of the 250kW
models for the SP310 Series. Since the 750kV system is used in common with all models, the numberof series connections of solar panels in a solar farm
can be uniﬁed. This greatly reduced the design work

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MEIDEN REVIEW Series No.169 2017 No.1

325 Max.

200 Max.

Electricalsystem3-phase 3-wireInsulation
systemPower frequency insulation transformer
systemRated output
power (kW )250(250kVA)

Rated output
voltage ( V )100(100kVA)
420/440

Rated output
current (A)344/329

Outputpower factor

0.99 or above(control for unity power factor)※ Leading as seen from PCS

Connection
cable size (sq)325 Max.

200 Max.

96.5

96.5

Conversion
efficiency (%)

138/131

Construction

Steel plate fabricated self-standing
outdoor panel (general outdoorspecifications)※ Without salt damage durabilityspecificationDimensions(mm)

W1300 × H2730
× D1200

W1000 × H2730
× D1200

Mass (kg)

2650

1750

Environment

panels account for almost 70% of the orders. Thus,
the air-cooled outdoor installation type PCS, SP310250T, was developed (Fig. 1). Further, there was noneed for adopting a double enclosure construction:
one for the PCS and other for the outdoor panel.
The light design made it easier to install. To tell thedifference between an outdoor and indoor PCS
model, the PCS type description was added with abranch number of an indoor “N” or outdoor “G.”[Example: SP310-250T-DN (for indoor type) andSP310-250T-DG (for outdoor type)]

AC output

As a result of outdoor installation type product development,
there was no need for adopting a double enclosure construction
and suspension work due to the weight limit.

SP310-100T-DG Remarks

MPPT operation voltage
range ( V )Connection
cable size (sq)Fig. 1SP310-250T-DG

Ambient
temperature(℃) / Relative
humidity (%)

At therated
outputAt therated
outputIP44−10〜40 / 5〜100burden for the customers. Table 1 shows speciﬁcations of the latest outdoor installation type 250kW(SP310-250T-DG) and 100kW (SP310-100T-DG)
models. Since the equipment conﬁguration of 250kW
and 100kW machines have been developed into a
uniﬁed product, horizontal development (having thesame features) among models becomes easy andwe can be ready for quick development against newfunctions (for example: new functions needed tomeet grid connection rules introduced in Section 3below) required for the PCS in the future.
To provide a good design harmonization
between 250kW and 100kW machines for easierinstallation work, the panel size of the 100kW modelSP310100T-DG

NP

Residual voltage (%)

SP310250T-DG

NPCenterof gravity

100UVR
tentativevalue
Continuous operation

3020%(SinceApril 2017)

Parallel off

Continued operation
or gate block
0.0(Voltage drop start)

1.0Time (s)(a) Voltage drop durability

600 or more

1300

600 or more

1000

with margin forinspection

with margin forinspection(a) Front elevation: 250kW model (left) and 100kW model (right)

Frequency (%)

Centerof gravity( ): for 60Hz

50.8(61.0)

Continuousoperation
Within 1s0.0(Frequency rise start)

0.06(0.05)
Time (s)1720: for maximum dimension
during transportation(b) Frequency regulation durability (step-up)

1700
1280

210

2730: for maximum dimension
during transportation

AirAirFrequency (%)

210

51.5(61.8)
50.0(60.0)
47.5(57.0)
Voltagedrop startContinuous
operation

Rate of change: ±2Hz/s

0.0(Voltage recovery)

1.0

Time (s)(c) Frequency regulation durability (ramp-up/down)Centerof gravity
Air1100 or morewith margin forinspection

Fig. 3Air

1200

1100 or morewith margin forinspection

FRT Voltage and Frequency Deviation RangeStipulated by the Grid-Interconnection Rule
JEAC 9701-2012

Since continued operation of power generation was required
even in the case of residual voltage 20% down, design change
was needed for the security of energy resources.

(b) Side view: 100kW model
Unit: mmFig. 2Outdoor Installation Type PCS: External Drawingof Panel Installation Side-by-Side

By unifying outer size (H × D) of maximum output 250kW machine(SP310-250T-DG) and 100kW machine (SP310-100T-DG), thepanel installation arrangement side-by-side becomes possible.

was made to ﬁt the 250kW PCS outdoor panel. We
can realize the installation of the 250kW and 100kW
model panels side-by-side. Fig. 2 shows an external drawing of side-by-side panel installation.

3 New Functions of PV PCS Neededfor Future Grid Connection Rules
As many solar farms started commercial operations by the enactment of the FIT System, provi-sion of new functions described below is needed forfuture PCS installations in order to easily clear theapproval of the grid-connection application from arelevant power company. This is from a viewpoint ofthe stable management of grid systems. It is anticipated that the PCS will be required to provide newfunctions in the future. Accordingly, the development of new functions is always indispensable.
Signiﬁcant necessary functions are introduced below.

3.1 Fault Ride Through (FRT) Function
The FRT function is the requirement to maintain PCS operation of power generation even under
the speciﬁed conditions of voltage drop or frequency deviation. Fig. 3 shows FRT Voltage andFrequency Deviation Range Stipulated by the gridconnection Rule JEAC 9701-2012.
MEIDEN REVIEW Series No.169 2017 No.127

Since the system voltage is stipulated to continue operation even though the voltage has lowered down below the rated voltage level by 20%, it
is necessary to secure the control voltage source inthe event of a voltage drop. For a solution in such acase, we developed a new model (D Series: the lastletters of the type description is -DN or -DG) that isapplicable without an Uninterruptible Power System(UPS). The scheme is that another new model (FSeries: the last letters of the type description is -FNor -FG) or part of solar panel generation (DC source)
is used as a direct control source from the DC side
while a UPS is installed inside or outside the PCS
unit. Presently, models of the D Series are used toprovide the FRT functions. Regarding frequency
deviation, the islanding operation sensor function of
the PCS is used to deﬁne the setup value of frequency deviation. To avoid wrong detection of anislanding operation, we reviewed the setup value ofthe frequency deviation speciﬁed for the FRT function.

3.2 Newly Developed Active Islanding Operation Sensor Function
If there is a power outage on the utility grid andit becomes an islanding operation, the solar farmside needs to detect this islanding operation andstop its power generation. Currently, the active
method of detecting islanding operation is different
among PCS suppliers. In the case of our PCS, thereactive power injection system is adopted. In thissystem, a small amount of reactive power in a periodic waveform, amounting to several percent ofequipment rating, is injected into the grid side sothat a frequency deviation in the grid system can becaused to detect the state of islanding operation by
the frequency change in the grid system. The PCS
in the solar farm is synchronized with the reactive
power injection timing, but if there is another solar
farm using reactive power injection type PCS in thesame grid network, there will be interference
between solar farms by the effect of reactive power
injection. It then becomes difﬁcult to accomplish
the detection of islanding operation. Because ofsuch a challenge, and due to necessity for fast parallel off upon the occurrence of islanding operation,
it is indispensable to install a new type of active
islanding operation sensor function (step-injection
frequency feedback type). We are now working onthe development of related products because thiswill become an imperative function in April 2017.

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3.3 Output Suppression Control Function
Based on Generation Forecast
Since the quantity of power generation at asolar farm is dependent on the weather, power generation operation during holidays continues like
operation during weekdays despite holidays having
a relatively less load demand. When the quantity ofsolar power generation exceeds the demand level,
the generation has to reduce. As such, we set up a
condition of output suppression to control power
generation in the unit of one whole day, per a requestof output suppression transmitted on the previous
day when demand on the next day is predicted to below. In addition, if the number of solar farms isincreased to affect the demand level in the future,
reverse tidal ﬂow is considered to occur in the timezone where power demand is small. In such a case,power suppression control is frequently required.
For this reason, the present program of output suppression in a one-day unit by means of manual ON/
OFF function is canceled and a new function of
remote operation for output suppression control in
the time unit shorter than one whole day will beadopted with the use of output command by calendar function. A provision of a better output control
functions will be the condition for grid connection
application approval in the future.

4 Additional Functions Needed for
Future PV PCS
Additional functions considered necessary in
the future are introduced below.

4.1 Self-Supporting Mode Operation Function
The self-supporting mode operation function isa function by which electric power generated by solar
panels can be utilized even in the middle of a power
outage from the grid. When the self-supporting
mode operation function is added to the PCS, thisPCS can be switched over to the self-supporting
mode and power can be used effectively. In thiscase, the PCS regularly supplying power to the grid
system according to the FIT System is switched overto the circuit of local load machines by changing thedestination of power supply at the time of a power
outage from the grid. Fig. 4 shows an example ofPCS system conﬁguration provided with a self-supporting mode operation function (rated voltage440V). As an emergency power source in the caseof a disaster, we are expecting a potential demandGrid connection line
Self-supporting load line

89RP
52RP

To self-supporting load
(3-phase 3-wire 440V)

6.6kV/440V
750kVA

Changeoverpanel
Grid system
MCCB

G1 MCCB

P1

Interlock(mechanical)

250kW
PCS

Fig. 4

Contact signal(No voltage
contact signal ofsystem parallel off)

250kW
PCS

250kW
PCS

Example of PCS System Configuration Provided
with Self-Supporting Mode Operation Function(Rated Voltage 440V )In the case of a power outage from the grid, self-supporting
mode operation is possible with a switchgear through which thePCS connection is switched over from the utility system to theautonomous load side.

for self-supporting mode operation function in thefuture. The SP310 Series shipped in June 2015 andthereafter is provided with the self-supporting mode
operation function. Even models of former types
can perform an interlinked operation with emergency generators. When an emergency generator isincluded in local load facilities, both self-supporting
mode operation and interlinked operation with anemergency generator can be performed.

4.2 Development of High-Performance
Products through Adoption of New TechnicalFactors
While we need to improve our products forconvenience, FIT-based prices are constantly lowering. Under such circumstances, the developmentof high-performance PCS is needed in the market.
Inverter elements used in PCS equipment are
now composed of Silicon (Si). As a high-performance material that is considered to replace Si,
Silicon Carbide (SiC) is getting high attention in themarket and active development programs are promoted in Japan for commercialization. If SiC inverters are adopted in the future, it is expected toimprove power conversion efﬁciency and reduce
PCS size as a result of inverter compact design. In

order to use capabilities of SiC inverters effectively,
inverter operation at high temperatures will become
necessary. For this reason, the mounting of SiC
inverters requires modiﬁcation of not only electricalcircuits but also peripheral components in terms ofthermal durability. Therefore, an entire perspectiveon the issues is needed for the development ofsuch products. The adoption of SiC inverters has
already begun for small-capacity PCS (up to 5kW)in the industry. Going forward, when the use of SiC
inverters in the PCS becomes common and thecapacity becomes bigger, there is a possibility thatthe adoption of the SiC inverter may go to industrial
PCS (up to 250kW).
As for other technological factors, we can indicate local cooling technologies to be used in PCS
equipment. Presently, the PCS to be delivered tocoastal areas is accommodated in an enclosed
package of air-conditioned type. When an enclosed
PCS panel construction is adopted and a concentrated cooling system is established to cool theheat-generating parts located inside the enclosure,
we consider that package-less versions can also bedelivered to salt hazard areas. Development of suchproducts, however, will require substantial modiﬁcation in structure. FIT-based prices tend to be reduced
year after year and requests for PCS price reduction
will be getting stronger. Since highly efﬁcient solar
farm operation will be required more in the future,development of products must be carried out withlong-term perspective.

5 Postscript
This paper introduced the present state of newmodel and function development regarding the PV
PCS, focused mainly on the four years after theenactment of the FIT System. Against the technicalbackground of new models and function developments, we can cite various factors: factors of solar
farm installation condition after the start of FIT, factors of grid connection rules where adding newfunctions in PV PCS is a must, and factors of customerʼs needs for more functions and higher performance. The business climate for photovoltaic generation is always changing. Going forward, to assureorders for the PV PCS, we need to keep working on
product development.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.

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