Technical Information SC2750-EV
Technical Information SC2750-EV
Technical Information SC2750-EV
The conversion efficiency of the inverter is defined by the ratio of AC output power to DC input power. The
main losses occur as waste heat due to switching and conducting losses inside the IGBT’s of the inverter and
due to the inductance of the sine filter choke. Depending on the methodology of measuring the efficiency,
the self-consumption of the inverter can also be integrated into the efficiency calculation as it is done with the
CEC efficiency rating.
The conversion efficiency strongly depends on the DC voltage with the highest efficiency being experienced
at the lowest possible DC voltage for this type of inverter bridge topology.
Table 1: Efficiencies without aux. losses at 25°C measured according to IEC 61683
CEC-Eta
Vmin @875Vdc: 98.43%
Vnom @957Vdc: 98.32%
Vmax @1200Vdc:98.06%
98,2
98,1
98,0
97,9
97,8
850 900 950 1000 1050 1100 1150 1200 1250
DC Voltage [V]
The inverter converts DC to AC power which requires some auxiliary power for the control, communication
and cooling system. The amount of auxiliary power depends on the ambient temperature and on the
produced output power. The auxiliary power is drawn from the AC side at the inverter terminals.
If the available PV power exceeds 100% of the DC power which can be converted by the inverter per
nameplate rating, the inverter produces some more AC power in order to compensate for its internal losses.
That way the effective auxiliary consumption of the inverter is 0 kVA as soon as the DC power exceeds
100%.
Figure 7: Harmonic distortion compared to the limits defined by IEEE 1547 and IEEE 519
Order 2 3 4 5 6 7 8 9 10
Lv/In[%] 0.09% 0.13% 0.17% 0.26% 0.06% 0.33% 0.15% 0.04% 0.07%
Order 11 12 13 14 15 16 17 18 19 20
Lv/In[%] 0.20% 0.03% 0.12% 0.05% 0.02% 0.06% 0.04% 0.06% 0.08% 0.09%
Order 21 22 23 24 25 26 27 28 29 30
Lv/In[%] 0.06% 0.09% 0.03% 0.06% 0.04% 0.03% 0.02% 0.01% 0.02% 0.01%
Order 31 32 33 34 35 36 37 38 39 40
Lv/In[%] 0.01% 0.01% 0.00% 0.02% 0.01% 0.01% 0.02% 0.00% 0.01% 0.03%
THDC
0.60%
Table 2: Harmonic distortion per phase at 1425 VDC and 100% PAC (60 Hz)
b) Measurements according to BDEW (50Hz)
Order 2 3 4 5 6 7 8 9 10
Lv/In[%] 0.13% 0.14% 0.26% 0.34% 0.10% 0.30% 0.15% 0.07% 0.19%
Order 11 12 13 14 15 16 17 18 19 20
Lv/In[%] 0.13% 0.02% 0.10% 0.06% 0.02% 0.04% 0.05% 0.02% 0.04% 0.05%
Order 21 22 23 24 25 26 27 28 29 30
Lv/In[%] 0.02% 0.05% 0.10% 0.02% 0.10% 0.10% 0.03% 0.06% 0.07% 0.01%
Order 31 32 33 34 35 36 37 38 39 40
Lv/In[%] 0.04% 0.03% 0.01% 0.01% 0.03% 0.00% 0.01% 0.02% 0.00% 0.01%
THDC
0.67%
Table 3: Total Harmonic distortion at 100% PAC (50 Hz)
The inverter can provide reactive power in addition to the active power which is produced by conversion of
incoming DC power. The resulting apparent power which is defined by the inverter’s nameplate rating is
calculated by geometric addition of reactive and active power.
The reactive power provision can be defined either via Power Factor (max. cosφ=0.8) or as a fix Q value.
Since the reactive power is independent of the active power provision of the inverter, it is possible to provide
the max. reactive power at any time respecting the limits defined by the apparent power value of the inverter
at different ambient temperatures. The inverter can provide up to 60% of its nameplate rating as reactive
power disconnecting only when the active power drops below 2 kW.
Reactive power has an impact on the frequency-dependent voltage drop at the sinus filter choke so that the
minimum MPP voltage depends on the applied power factor. This effect is illustrated in the below pictures.
2.75MVA
Cos φ= 0.845
2.250 MW
1.582 MVAr
Figure 10: P/Q diagram at 35°C and grid voltage U ≥Un Figure 11: P/Q diagram at 35°C and U=0.9Un
b) P/Q diagram SC 2750-EV(-US) @50°C
Figure 12: P/Q diagram at 50°C and grid voltage U ≥Un Figure 13: P/Q diagram at 50°C and U=0.9Un
c) Minimum MPP Voltage with reactive power @60 Hz
The thermal management of the inverter decides about de-rating conditions in dependence of ambient
temperature, DC voltage and altitude.
Above 35°C the output power of the inverter has to be reduced. High DC voltage causes switching losses
at the IGBTs which significantly contribute to the heat rise inside the inverter. With rising ambient temperature
the maximum operation DC voltage with full load needs to be reduced between 25°C and 50°C in order
to support the inverter’s thermal management.
The lower density of air with rising altitude reduces the cooling effect. The inverter can produce its full power
output at altitudes up to 2,000m with only reducing slightly the max. temperature for operation with nominal
power. An adaptation starts above 1,000m and results in a linear shift to lower max. temperature also
aligned with the temperature drop at high altitudes.
2500
2000
MPP@50°C
1500
MPP@35°C
MPP@25°C
1000
500
0
800 900 1000 1100 1200 1300 1400 1500
Figure 18: De-rating depending on DC voltage
b) De-rating at high Altitudes
The inverter has the capability to support the grid by remaining online or by reactive power feed-in during a
temporary change of the grid voltage beyond preset low voltage (LV) and high voltage (HV) thresholds. The
below figure describes the max. voltage ride-through (VRT) capabilities of the SC 2750-EV(-US). If the max.
disconnecting delay time at specific voltage levels is exceeded, the inverter switches off and reconnects to
the grid when the voltage returns to the preset nominal operation window.
A project specific VRT window can be defined with the parameters described in the inverter’s operation
manual.
The inverter will also ride through abnormal frequency events with the capability of reducing the output
power at high frequency scenarios. The ride-through capabilities are described below with similar
possibilities to adjust the window as for the voltage ride-through.
i. A. Daniel Greger
Product Manager
i. A. Andreas Tügel
Product Manager