4 System Planning – Electrical
4.1 Introduction
The aim of this section is to provide general information
for planning integration of the inverter into a PV system:
•
PV system design, including earthing
•
AC grid connection requirements; including
choice of AC cable protection
•
Ambient conditions, e.g. ventilation
4.2 DC
Side
4.2.1 Requirements for PV Connection
The specifications for PV connection are shown in
Parameter
MLX 60
MPP trackers/Inputs per MPPT
1/1 (external string combining)
Maximum input voltage, open
circuit (V
dcmax
)
1000 V
Input voltage range
565–1000 V @ 400 Vac
680–1000 V @ 480 Vac
Rated voltage DC
630 V @ 400 Vac
710 V @ 480 Vac
MPPT voltage range - rated
power
570–800 V @ 400 Vac
685–800 V @ 480 Vac
Max. MPPT current DC
110 A
Max. short circuit current DC
150 A
Table 4.1 PV Operating Conditions
Illustration 4.1 Operating Range per MPP Tracker
To avoid damaging the inverter, observe the limits in
when dimensioning the PV generator for the
inverter.
CAUTION
Always observe local requirements, rules, and
regulations for the installation.
4.2.1.1 Maximum Open-circuit Voltage
The open-circuit voltage from the PV strings must not
exceed the maximum open-circuit voltage limit of the
inverter. Calculate the open-circuit voltage at the lowest
PV module operating temperature expected for the
location. If the module operating temperature is not well-
defined, check local common practice. This calculation
implies a maximum of 23–26 modules per string, for
standard 60-cells c-Si modules. It depends on the local
climate, module model, and installation conditions (for
example ground based or flush mounted). Also check that
the maximum system voltage of the PV modules is not
exceeded.
Special requirements apply to thin-film modules. See
4.2.1.2 MPP Voltage
The string MPP voltage must be within the operational
range of the inverter MPPT. Operational range is defined
by:
•
Minimum voltage operation MPP:
-
570 V @ 400 V
ac
-
685 V @ 480 V
ac
-
Other grid voltages: Estimate by
‘√2 x grid voltage [V
ac
]’
•
Maximum voltage operating MPP (800 V), for the
temperature range of the PV modules
This requirement implies a minimum of 23–25 modules per
string, for standard 60-cells c-Si modules. It depends on
the location, module model, installation conditions, and
grid voltage. If the input DC voltage is below the minimum
MPP voltage for a period, the inverter will not trip but shift
the operation up to the minimum voltage operation MPP,
resulting in some yield losses.
MPP of the inverter can be below the minimum voltage
operation MPP due to circumstances like:
•
High cell temperature
•
Partial shading conditions
System Planning – Electrica...
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L00410648-02_02 / Rev. date: 2014-10-03
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