04 wachtel - overview about different communication protocols for pv-hybrid systems

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

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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


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Modbus Protocol-StackLayer 7 application protocol



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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.

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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

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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

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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

04 wachtel - overview about different communication protocols for pv-hybrid systems

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