SMA MLX 60, MLX 60 UL, MLX Series Design Manual
SMA Solar Technology AG
Solar Inverters
MLX Series
Design Guide
www.SMA.de
Contents
Contents
1 Introduction
1.1 Introduction
1.2 List of Abbreviations
2 Inverter Overview
2.1 Product Label
2.2 Mechanical Overview of the Inverter
2.3 Description of the Inverter
2.3.1 System Overview 6
2.3.2 Functional Safety 8
2.3.3 Operation Modes 9
2.4 MPP Tracker and Derating
2.4.1 MPP Tracker 10
2.4.2 Inverter Derating 10
2.4.3 Power Reference 10
2.5 Grid Code
2.5.1 Grid Protection Settings 12
2.6 Grid Support (Ancillary Services)
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2.6.1 Fault Ride Through 12
2.6.2 Reactive Power Management 13
2.6.3 Active Power Management 14
2.7 Functional Safety Settings
3 System Planning – Mechanical
3.1 Unpacking
3.2 Installation
3.2.1 Installation Conditions
3.3 Mounting the Inverter
3.3.1 How to Position the Inverter 18
3.3.2 Torque Specifications for Installation
3.4 Cable Specifications
4 System Planning – Electrical
4.1 Introduction
4.2 DC Side
4.2.1 Requirements for PV Connection 20
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4.2.1.1 Maximum Open-circuit Voltage 20
4.2.1.2 MPP Voltage 20
4.2.1.3 Short-circuit Current 21
4.2.1.4 MPP Current 21
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Contents
4.2.1.5 PV to Earth Resistance 21
4.2.1.6 Earthing 21
4.2.1.7 Parallel Connection of PV Arrays 21
4.2.1.8 PV Cable Dimensions and Layout 21
4.2.2 Determining Sizing Factor for PV Systems 22
4.2.3 Thin Film 22
4.2.4 Internal Surge Overvoltage Protection 22
4.2.5 Thermal Management 23
4.2.6 Simulation of PV 23
4.2.7 PV Field Capacitance 23
4.3 AC Side
4.3.1 Requirements for AC Connection 24
4.3.2 AC Connection Protection 24
4.3.3 Grid Impedance 25
4.3.4 AC Cable Considerations 25
5 Communication and System Planning, Inverter Manager
5.1 Ethernet Communication
5.1.1 System Overview 26
5.1.2 Inverter Manager 26
5.2 User Interfaces
5.3 I/O Box
5.4 Weather Station
6 Technical Data
6.1 Technical Data
6.2 Derating Limits
6.3 Norms and Standards
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6.4 Mains Circuit Specifications
6.5 Auxiliary Interface Specifications
6.6 Ethernet Connections
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Introduction
1Introduction
1
1
1.1 Introduction
The Design Guide provides information required for
planning and dimensioning an installation. It describes
requirements for use of the MLX series inverters in solar
energy applications.
Illustration 1.1 MLX Inverter
Additional resources available:
Installation Guide, supplied with the inverter, for
•
information required to install and commission
the inverter
Inverter Manager Installation Poster, for
•
information required to install the Inverter
Manager
Inverter Manager Assembly Installation Guide, for
•
information required to install the Inverter
Manager Assembly
Fan Installation Instruction, for information
•
required to replace a fan
SPD Installation Instruction, for information
•
required to replace Surge Protection Devices
These documents are available from the download area at
www.sma.de, or from the supplier of the solar inverter.
Additional application-specific information is available at
the same location.
1.2 List of Abbreviations
Abbreviation Description
ANSI American National Standards Institute
AWG American Wire Gauge
cat5e Category 5 twisted pair cable (enhanced)
DHCP Dynamic Host Configuration Protocol
DNO Distribution Network Operator
DSL Digital Subscriber Line
EMC (Directive) Electromagnetic Compatibility Directive
ESD Electrostatic Discharge
FCC Federal Communications Commission
FRT Fault Ride Through
GSM Global System for Mobile Communications
HDD Hard Disk Drive
IEC International Electrotechnical Commission
IT Isolated Terra
LCS Local Commissioning and Service
LED Light-Emitting Diode
LVD (Directive) Low Voltage Directive
MCB Miniature Circuit Breaker
MPP Maximum Power Point
MPPT Maximum Power Point Tracking
NFPA National Fire Protection Association
P P is the symbol for active power and is
measured in Watts (W).
PCB Printed Circuit Board
PCC Point of Common Coupling
The point on the public electricity network to
which other customers are, or could be,
connected.
PE Protective Earth
PELV Protected Extra-Low Voltage
PLA Power Level Adjustment
P
NOM
POC Point of Connection
P
STC
PV Photovoltaic, photovoltaic cells
RCD Residual-Current Device
RCMU Residual Current Monitoring Unit
R
ISO
ROCOF Rate Of Change Of Frequency
Q Q is the symbol for reactive power and is
S S is the symbol for apparent power and is
Power [W], Nominal conditions
The point at which the PV system is connected
to the public electricity grid.
Power [W], Standard Test Conditions
Insulation Resistance
measured in reactive volt-amperes (VAr).
measured in volt-amperes (VA).
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Introduction
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Abbreviation Description
STC Standard Test Conditions
SW Software
THD Total Harmonic Distortion
TN-S Terra Neutral - Separate. AC Network
TN-C Terra Neutral - Combined. AC Network
TN-C-S Terra Neutral - Combined - Separate. AC
Network
TT Terra Terra. AC Network
Table 1.1 Abbreviations
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Inverter Overview
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2 Inverter Overview
2.1 Product Label
Illustration 2.1 Product Label MLX 60
The product label on the side of the inverter shows:
Inverter type
•
Important specifications
•
Serial number, located under the bar code, for
•
inverter identification
2.2 Mechanical Overview of the Inverter
2
Illustration 2.2 Product Label MLX 60 UL
1 Cover for installation area
2Front cover
3 Die-cast aluminium heat sink
4Mounting plate
5 Display (read-only)
6 PV load switch (optional)
7Fans
Illustration 2.3 Mechanical Overview of the Inverter
2.3 Description of the Inverter
Inverter features:
IP65 enclosure/Type 3R
•
PV load switch
•
Ancillary service functionalities
•
Transformerless
•
3-phase
•
3-level inverter bridge with a high performance
•
Integrated residual current monitoring unit.
•
Insulation test functionality.
•
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Inverter Overview
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Extended fault ride through capabilities (to
•
support reliable power generation during grid
faults) - depending on inverter configuration
Compliant with a wide range of international
•
grids
Adapted to local requirements and conditions via
•
grid code setting
2.3.1 System Overview
The MLX system draws on the advantages of both string
inverters and central inverters, making it highly applicable
in many commercial and utility scale plants.
The MLX system consists of the MLX inverter itself, a DC
string combiner and the Inverter Manager.
The communication network of an MLX system is divided
into 2 Ethernet networks; Plant network and inverter
network. The plant network is the communication interface
to the MLX plant and may be shared by several Inverter
Managers as well as other IT equipment, while the inverter
network is solely used for MLX inverters. The plant network
must have a DHCP server (router) as the Inverter Manager
requires automatic IP assignment. It is recommended to
use professional grade routers and switches. The Inverter
Manager provides:
Control of up to 42 MLX inverters
•
Single point of access for each (up to) 2.5 MVA
•
plant for simple plant network deployment
Easy commissioning and service of the plant
•
using the Local Commissioning and Service (LCS)
tool
Safe upload to data warehouse services, and
•
control of all local requirements and settings
from the DNO
Open source Modbus TCP communication
•
protocol using SunSpec Alliance profile via
Ethernet both for monitoring and control, making
it easy to integrate in e.g. SCADA systems
Grid management interface through the optional
•
I/O box for PLA and reactive power commands
Easy integration of meteorological data using an
•
RS-485 SunSpec Alliance compliant weather
station
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Inverter Overview
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2
1PV strings
2DC combiner
3MLX inverter
4MLX Inverter Manager
5Router
6LCS tool
7Portal
8SCADA system
9 Weather station
10 I/O box
11 Grid management
12 Transformer station
Illustration 2.4 System Overview
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Inverter Overview
Illustration 2.5 Overview of Installation Area
PELV (Safe to touch)
2 Equipment grounding
7 Ethernet interface x 2
8 RS-485 interface (not in use)
Live Part
1 AC connection terminals
5 PV connection terminals
Other
3Surge Protection AC
4Surge Protection DC
6 PV load switch (optional)
2.3.2 Functional Safety
The inverter is designed for international use, with
functional safety circuit design meeting a wide range of
international requirements (see 2.5 Grid Code).
Single-fault Immunity
The functional safety circuit has a fully redundant built-in
single-fault detection. If a fault occurs, the inverter
disconnects from the grid immediately. The method is
active and covers all circuitry within the residual current
monitoring, both for continuous levels and sudden
changes. All functional safety circuits are tested during
start-up to ensure safe operation. If a circuit fails more
than 1 out of 3 times during the self-test, the inverter
enters fail safe mode. If the measured grid voltages, grid
frequencies, or residual current during normal operation
differ too much between the 2 independent circuits, the
inverter ceases to energise the grid and repeats the selftest. The functional safety circuits are always activated and
cannot be disabled.
Isolation
During the self-test, the inverter has an isolation measuring
system that detects whether the isolation in the PV system
is above the required level. This is done before the inverter
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Inverter Overview
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starts to energise the grid. During grid connection, the
inverter measures the continuous leakage current in the
system. If this level is exceeded more than 4 times during
24 hours, the inverter stops operating due to safety
hazards in the PV system.
NOTICE
Depending on the local legislation, a minimum earth-toPV isolation resistance is defined. A typical value is
82 kΩ.
Self-test
The insulation resistance between the PV arrays and earth
is also tested during the self-test. The inverter does not
energise the grid if the resistance is too low. It then waits
10 minutes before making a new attempt to energise the
grid.
Residual current
Residual current is continuously monitored. The inverter
ceases to energise the grid when:
The cycle RMS value of the residual current
•
violates the trip settings for more than the
duration of ‘clearance time’, or
A sudden jump in the residual current is detected
•
Grid Surveillance
Grid-related parameters are under constant surveillance
when the inverter energises the grid. The following is
monitored:
Grid voltage magnitude (instantaneous and 10
•
minute average)
Grid voltage and frequency
•
Loss of Mains (Islanding detection):
•
3-phase Loss of Mains (LoM) detection
•
Rate of Change of Frequency (ROCOF)
•
Frequency shift.
•
DC content of grid current
•
Residual current by means of RCMU
•
The inverter ceases to energise the grid if one of the
parameters violates the grid code.
Status LEDs
Green
Off grid
Connecting
On grid
Internal inverter event
Fail safe
Table 2.1
Off grid (standby) (LEDs off)
#0-51.
When no power has been delivered to the AC grid for
more than 10 minutes, the inverter disconnects from the
grid and shuts down. User and communication interfaces
remain powered for communication purposes.
Connecting (Green LED flashing)
#52-53.
The inverter starts up when the PV input voltage reaches
the minimum DC feed-in voltage. The inverter performs a
series of internal self-tests, including measurement of the
resistance between the PV arrays and earth. Meanwhile, it
also monitors the grid parameters. When the grid
parameters have been within the specifications for the
required amount of time (depends on grid code), the
inverter starts to energise the grid.
On grid (Green LED on)
#60.
The inverter is connected to the grid and energises the
grid. The inverter disconnects when:
it detects abnormal grid conditions (dependent
•
on grid code), or
an internal event occurs, or
•
PV power is insufficient (no power is supplied to
•
the grid for 10 minutes)
The inverter then enters connecting mode or off grid
mode.
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Green
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Red
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Green
Red
Green
Red
Green
Red
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2.3.3 Operation Modes
The inverter has 5 operation modes, indicated by LEDs.
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Internal Inverter Event (Green LED flashing)
#54
The inverter is waiting for an internal condition to become
within limits (for example a too high temperature) before
it will go back on grid.
Fail Safe (Red LED flashing)
#70.
If the inverter detects an error in its circuits during the selftest (in connecting mode) or during operation, the inverter
goes into fail safe mode, disconnecting from grid. The
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