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7/30/2019 04 Wachtel - Overview About Different Communication Protocols for PV-Hybrid Systems
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Fraunhofer ISE
Overview about different CommunicationProtocols for PV-Hybrid Systems
Jakob Wachtel M.Sc.
Department PV Off-Grid Solutions and
Battery System Technology
Fraunhofer Institute for
Solar Energy Systems ISE
Chambry, April 26th 2012
6th European Conference PV-Hybrid and Mini-Grid
Fraunhofer ISE
2/26
Outline
ISO-OSI Reference Model
RS-485 / Modbus / SunSpec
CAN / CANopen
IEC-61850
Wireless Solutions
Conclusions
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ISO-OSI Reference Model
7. Application Layer 7. Application Layer
6. Presentation Layer 6. Presentation Layer
5. Session Layer 5. Session Layer
4. Transport Layer 4. Transport Layer
3. Network Layer 3. Network Layer
2. Data Link Layer 2. Data Link Layer
1. Physical Layer 1. Physical Layer
Data Transmission
Application Process 1 Application Process 2
Data
Data
Data
Data
Data
Data
Data
Data
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Modbus
Master/Slave-Architecture for asynchronous serial connections (EIA/TIA-485-
A, -232-E, EIA-422)
Client/Server-Architecture for
interconnection of different
networks via gateways All communication is initiated
by Modbus master
No intercommunication
between slaves possible
Architecture
Quelle: MODBUS Application Protocol Specification V1.1b
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Modbus
Simple signal oriented protocol
The meaning of the telegram is given by the data type, a function code and a
numerical address.
Wide spread
Openly
published
Royalty-free
Protocol
Quelle: MODBUS Application Protocol Specification V1.1b
Fraunhofer ISE
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Modbus Protocol-StackLayer 7 application protocol
Quelle: MODBUS Application Protocol Specification V1.1b
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SunSpec Alliance
American initiative, also european members (Fronius, SMA, Kaco), foundedin July 2009
Communication for PV Systems (on- and off-grid)
Uses Modbus and defines several profiles
Collaborates with ZigBee, IEC 61850, DNP3 (telecontrol)
First specifications comprise
Common models
Inverter models
Meter models Environmental models
String combiner models
So far only monitoring is considered. For control there is a plan in place.
Fraunhofer ISE
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Controller Area Network
Covers layers 1 and 2 of ISO-OSI reference
model
Developed by BOSCH in 1983 and quickly
became the leading field bus protocol for
the automobile industry
Differential bus (2 wire twisted
pair) known for its robustness
Multimaster capable, many nodes may
simultaneously access the bus
Bus length proportional to bitrate
One unique CAN-ID plus eight data bytes
Bitrate [kbit/s] Bus length [m]
10 5000
20 2500
50 1000
125 500
250 250
500 100
1000 25
CAN-IDb
1
b
2
b
3
b
4
B
5
b
6
b
7
b
8
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CANopen
Object oriented approach
Application layer protocol that is defined in profiles
DS 301 is the main profile defining basic communication services
Other profiles describe optional CANopen services
Device Profiles: Describe the functionality of one device
CiA 401: Generic I/O
Application Profiles
CiA 437 Photovoltaic Systems
CiA 454 Energy Management Systems
Fraunhofer ISE
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CANopen Basic Services
Network management (MNT): One NMT Master controls all NMT Slaves
Error control: Monitoring of nodes (heartbeat)
Synchronisation: One SYNC-producer sends synchronisation telegrams
Process data objects (PDO): Send process data
Preconfigured through configuration and mapping parameters
Enables the usage of pure CAN (all eight data bytes for process data)
One Producer, any number of consumers
Service data objects (SDO): Access to object dictionary
Confirmed client / server principle
Four bytes needed to address object dictionary entry
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CiA 454 Energy Management Systems
Describes the typical devices of a PV-hybrid off-grid energy supply system
Tries to be as concrete as possible but as abstract as needed
Provides standardised interface for these devices which are
Energy storage (battery)
Voltage converter (charge controller, inverter, )
Load
Generator
These descriptions / abstract specifications enable a superordinate energymanagement.
Different operation modes increase system availability.
Application Profile for PV-hybrid Off-grid Systems
Fraunhofer ISE
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Modes of Operation
NormalEMS gathers data, schedules
energetic interchange and
controls components.
MasterlessBattery broadcasts SOC,
components dicide locally whether
to switch on or off
CommunicationlessComponents measure voltage
(or frequenzy) and dicide locally
whether to switch on or off.
No EMSEMS available
Communication okCommunication
failure
Some systems do not need asophisticated EMS.
The EMS may have a failure.
Some components must be
operable even when nocommunication is foreseen.
If there is a broken wire
operation should still be possible
to a minimum extent.
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Network Management with Plug and PlayAbility
Node IDs are assigned via LSS fastscan
service
Node IDs are assigned consecutively by the
network manager / energy managementsystem (EMS) which always has NID 1.
Device identification is realised by an object
called supported virtual devices (6000h)
which amongst others contains a bit field
Virtual device function (VDF).
According to the VDF, the EMS integrates the
device into its control strategy.
Instance
Offset
Instance
Number VDF
Voltage
Converter
Genera-
torBatteryLoad
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Loads
Non-controllable loads
E.g. consumer electronics must
always be available when needed.
Controllable loads
E.g. water pumps may be switched on in times of excess
power generation through stochastic generators.
Influenceable loads
E.g. the switching of a washing
machine may be shifted in time.
Variable in power
E.g. a freezer may vary its temperature
according to energy availability
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Power Generators
Stochastic
Power generators that use
renewable resources
Controllable
Backup Diesel generator
Variable in power
Both stochastic and
controllable generators may
be variable in their powerproduction.
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network control
station A
Substation (e.g. distribution station)
60870-5-104
Substation control computer
Switchboard with
controller ...Transformer controller
IEC 60870-5-104 or e.g. Profibus
Planned to be
exchanged by
IEC-61850
network control
station BIEC 60870-6
IEC 61850 Background
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Started in 1995 as a standardisation project
Originally developed for the substation internal communication
IEC 60870 signal oriented: every telegram corresponds to one data point (e.g. onemeasurement value or message), for interoperability profiles are needed
Replacement of IEC 60870
Advantages of IEC 61850:
Object oriented data model
Devices are able to discribe themselves: Structure of the data model can becommunicated via the protocol
In China and USA already often in use (substations)
Extension for monitoring / control of :
Wind turbines (IEC 61400-25)
Hydroelectric power plants (IEC 61850-7-410)
Distributed energy resources (IEC 61850-7-420) (including PV)
Background IEC 61850
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Services defined in IEC 61850
Server connections
Retrieval of information about the data model
Setting and reading of measurement, status and control values
Grouping of data for faster access
Reporting and configuration of reports
Logging and configuration von logs
File transmission
Time synchronisation
Mapping
MMS or
SOAP
Energy GatewayMaintenance firm /
network operator /
web portalIEC 61850 Server
PV Model FieldbusDriver
IEC 61850 Client
IEC 61850 Services
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Data Models for Decentralised EnergyResources
Data models for DER can be assembled from the LN samples from
IEC 61850-7-4: General LNs for current and voltage measurement / controldevices, etc.
IEC 61400-25: Specific LNs for wind turbines
IEC 61850-7-410: Specific LNs for hydropower plants
IEC 61850-7-420: Specific LNs and distributed generation technology (photovoltaic,CHP, emergency generators, generators, power converters, thermal storage,battery storage, additional measuring devices)
High degrees of freedom to model a specific system in detail
Abstract nodes that allow a handling regardless of the specific technology used
Differently detailed data models for different applications (monitoring, integration intovirtual power plants, etc) in one device
Until now, a "plug and play" integration is not provided in the norm. Rather, anintegration of the control technology via comfortable engineering tools was foreseen.
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IEC 61850 Model Hierarchy
Logical DeviceFreely selectable
Server
Logical Node61850-7-4, 61850-7-420
Data Object61850-7-3
Data Attribute61850-7-3/2
1
1-n
1
2-n
1
1-n1
0-n
1
0-n
1
1-n
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IEC 61850 Review
Highly flexible
Can be mapped to different protocols
All pervasive, everyone talks about it
High complexity, awkwardly defined protocol
Partly not unambiguous and faulty
Too many degrees of freedom for the creation of models (avoidsinteroperability between different manufacturers devices).
The creation of profiles for specific plant types and parties is useful andnecessary for manufacturer comprehensive compatibility.
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Wireless Solutions
Many proprietary solutions exist that cover all protocol layers (Z-Wave,Enocean)
IEEE 802.15.4 is a promising international standard
Properties are low ranges, low energy consumption, small data rate, low cost
Slow communication
Not deterministic,
not hard real-time
capable
Cannot replace afieldbus protocol
Physical Layer
MAC Layer
Network Layer
Application Layer
IEEE 802.15.4
E.g. ZigBee, 6LoWPAN,
WirelessHART
E.g. ZigBee Smart Energy Profile,
Smart Energy Profile 2.0
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Wireless SolutionsIEEE 802.15.4
RFD
FFDRFD
RFD
FFD
FFD
Full Function Device (FFD) can route packets but does not work with battery
supply solely
Reduced Function Device (RFD) can only communicate with one FFD,sleeps most of the time, very little energy consumption
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Alliance founded in 2002
Interfaces IEEE 802.15.4
Defines profiles for data exchange for specific applications, one is the Smart
Energy Profile
However, many ZigBee products use proprietary profiles that are not provenby the ZigBee alliance
Promising development: Smart Energy Profile 2.0 (advocated by NIST) canalso interface other protocols (e.g. TCP/IP)
Shows its strengths in dense meshed networks
ZigBee
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Summary
Use standards!
Either use CAN or RS-485 and define a proprietary protocol on top or use
CANopen or Sunspec for application layer protocols.
In the field either Sunspec or CANopen seem to be the most feasible
solutions.
For a coherent and robust communication infrastructure use CANopen.
For quick starts and smaller systems Modbus / Sunspec might be the right
choice due to its simplicity.
IEC 61850 is not mature but in the future seems to prevail and become thenumber one standard for on-grid systems, substation internal and external
communication.
Wireless communication should only be used for slow communication without
high demand in reliability.
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Thank You for Your Attention!
Jakob Wachtel, M.Sc.
[email protected]+49(0)761-4588-5425
Fraunhofer Institute for Solar Energy Systems ISE