power quality and protect other equipment
connected to the grid.
U1 Fixed
U2 Trip Limit
Illustration 2.8 Grid Voltage above Limit Set by DNO
Derating - Grid Over-frequency
The output power is reduced as a variable of the grid
frequency. There are 2 methods for reducing the output
power: ramp and hysteresis. The grid code setting
determines which method is implemented in a specific
installation.
Primary frequency control – ramp method
See
.
The inverter reduces output power if the grid frequency
exceeds f1. Reduction occurs at a preconfigured rate,
which is the ramp (R) shown in
. When the
frequency reaches f2, the inverter disconnects from grid.
When the frequency decreases below f2, the Inverter
reconnects to grid and ramps up power at the same rate
as for the reduction.
Illustration 2.9 Primary Frequency Control – Ramp Method
Primary frequency control - hysteresis method
See
.
To support grid stabilisation, the inverter reduces output
power if the grid frequency exceeds f1. Reduction occurs
at a preconfigured rate, which is the ramp (R) shown in
. The reduced output power limit is
maintained until the grid frequency has decreased to f2.
When the grid frequency has decreased to f2, the inverter
output power increases again following a time ramp T. If
the grid frequency continues to increase, the inverter
disconnects at f3. When the frequency decreases below f2,
the inverter reconnects to grid and ramps up power at the
same rate as for the reduction.
Illustration 2.10 Primary Frequency Control – Hysteresis
Method
2.5 Grid
Code
The MLX grid code file contains settings that determine
both the behaviour of the single inverter and the entire
plant. The grid code file is divided into 2 main sections:
•
Grid protection settings
•
Grid support (ancillary services)
The LCS tool used for commissioning the inverter is
equipped with a range of default grid codes to meet
national requirements. Changing these default grid code
parameters requires a customised grid code file, supplied
by SMA. See
2.7 Functional Safety Settings
about how to
apply for customised grid code parameters.
NOTICE
Obtain approval from the local distribution network
operator (DNO) before connecting the inverter to the
grid.
Inverter Overview
L00410648-02_02 / Rev. date: 2014-10-03
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