ABB AB, Corporate Research - 1 7/02/08
Reglering över trådlös länk
Alf Isaksson
ABB Corporate Research
Jerker Delsing
Luleå University of Technology
orate Research - 2
Outline
Characteristics of Process Automation
Benefits of wireless technologies
Requirements on wireless communication
Control communication
Current situation
ABB WISA
Wireless Hart
Challenges & requirements wireless control
The SOCRADES project
Summary
ABB AB, Corporate Research - 3
Characteristics of process automation
Many control loops (>100)
90 % or more are under PI control
Model based tuning not yet standard
Increasing amount of sensors
Automation is an increasing part of a green field investment, and wiring may be a significant part of this
Equipment are in well defined locations – not ”Ad hoc” networks
orate Research - 4
Characteristics cont´d
Most loops are relatively slow (sampling interval 1 s or slower).
Exceptions are e.g. drive systems and rolling mills (sampling time 10-20 ms)
Most processes open-loop stable. Exceptions are e.g. level control, exothermic reactors.
K(s) C(s)
+ -
Motor Speed ωm
Motor Torque
Tm Speed
Reference ωref
Load Torque Disturbance
Tl Motor
Jm cm
Load Jl cl Shaft
ks cs
Load Speed
ωl
Controller (PI)
Converter (Non- Minimum
Mechanical system G(s)
ABB AB, Corporate Research - 5
Wireless Communication Requirements
Node Density
Potentially hundreds within one
controller (gateway), thousands within a plant
Bandwidth
Typically moderate bit rate
Latency
Short and deterministic delays
Power Consumption
Low consumption to enable wireless powering
Operating Frequency
License free band above 1 GHz
Interference
Industrial Environment
Electromagnetic Interference (EMI)
Other Wireless Systems
1 2 3 300-500
. . .
~ 15 ms
How?
orate Research - 6
Control communication today -- Network Architecture
MCC
Variable Speed Drives
S800 I/O
S900 I/O (Ex) Workplaces
Control Network
Remote Clients
System Servers
Fieldbus High Speed Linking Devices
Process Automation Process
Automation and Safety
Operator Engineering
Maintenance
Safety
ABB AB, Corporate Research - 7
Control communication history
1870 195
0:s ~1961 ~1988 20
07
Digital controlcommunication busesISA S50.02 standard
Digital electrical com.RS- 232 standard
4-20 mA analog communication standard
Mechanical and pneumatic controlcommunication Wireless Hart standard
2006
ABB WISA
Bluetooth
1998
orate Research - 8
Primary coil
MF-primary power supply
Secondary coil/
power receiver
“Coreless”
Transformer
ABB WISA: Com & power for Manufacturing
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Which „Wireless“-Technology?
Standards: Not developed for Industrial automation*
Requirements:
High node number/density
Real time suited
Short, guaranteed latency
Indep. of node number
-> highest reliability
Low power consumption
(* Exception: ZigBee – not for real time factory automation)
200k 712k 1M 11M 22M 54M bit/s
Power Consumption, Cost, Complexity in typ. Automation Application >300<300<20<1 mW
WLAN
<100m 802.15.1
Bluetooth
(2.45GHz)
802.11a/HL2
(5.2 GHz)
802.15.4 ZigBee
(2.45GHz)
Data Rate
802.11g
(2.45GHz)
802.11b
(2.45GHz)
WISA: Wireless Interface for Sensors and Actuators
WISA 802.15.1 phys
(2,45GHz)
orate Research - 10
WISA System Structure: Cells and Nodes
WISA-Com organizes
communication in „cells“
One cell consists of
Communication nodes (e.g.
wireless proximity switches)
One Base Station controlling the communication and
providing data access to a control system
A complete WISA-COM system can consist of several
overlapping cells
node node
node node
Base Station
Control system downlink
uplink
Base Station A node-A1
node-A1
node-B1
Base Station B
node-Bj node-B1
node-Ai
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WirelessHART -- OSI Layers
orate Research - 12
WirelessHART Networks
Network manager
One manager for each network
Gateway
Connects mesh network to host application
Field devices
Process connected devices
Network Manager
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Benefits of Wireless Technologies
Reduced wiring, terminals, I/O blocks, cabinets…
Reduced design and installation work
No cable wear and tear
No connector failure
Harsh environments
No mechanical design limitations
Mobile, moving, rotating production equipment
Fast commissioning and reconfiguration
Why?
orate Research - 14
WirelessHART Network Resources
Superframe, slots, and transactions
TDMA
Reserved slots
CSMA
Shared slots
Contention based access - collisions are possible
Superframe
time
STX
ACK
Transaction slot
ABB AB, Corporate Research - 15
WirelessHART Performance
Slot
10 ms
Packet payload size
~ 80 - 90 bytes / packet
Transmission rate
1 packet / superframe (cycle)
Minimum superframe length is 0.5 s
Maximum size of a Network
250 nodes / Gateway
≤ 8 hops deep
99.9% data delivery reliability
Due to redundant paths (mesh) and retransmissions
orate Research - 16
Simulation Example – DC position servo
Blue (star)– perfect sync communication & control
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Wireless Process Control -- Challenges & Requirements
No standard specifies control
Control has to be fault tolerant against
Temporary communication outage
Complete loss of communication
Fluctuations in communication delay
Need to limit amount of communication
Synchronization becomes issue: Event-based control?
Must not increase user complexity significantly, e.g.
Still PID control
Minimum of configuration parameters
User should not be expected to provide process model
orate Research - 18
Control delays in Wireless Hart
time
time
time
S A S
C
C Wireless Hart superframe
Controller in sync
Controller out of sync
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Control performance as function of T & D
Communication delay gives performance degradation if T< 2 and D<2
G s =Ke−Ds Ts1 IAE =
∫
0
∞
∣et ∣dt
orate Research - 20
Performance as function of Kv & D
G s = Kve−Ds s
ABB AB, Corporate Research - 21
Delay compensation in Wireless Hart
Conclusion: Delays due to synchronization only problem
for corner cases. Quite possible to compensate but clearly better to synchronize communication with controller.
orate Research - 22
Packet loss compensation in Wireless Hart
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Disturbance rejection with packets lost
Conclusion: Difficult to compensate packet loss by prediction.
Basically, when you have no communication you have no feedback!
orate Research - 24
Socrades
Service-Oriented Cross-layer infRAstructure for Distributed smart Embedded deviceS
Large EU project
9 M€, 3 year
Partners
ABB, Siemens, Schneider, SAP, Boliden, ....
LTU, KTH, IFAK, POLIMI, TUT, Lboro, ....
ABB AB, Corporate Research - 25
Control over wireless link -- WP4
Develop the continuous manufacturing device
infrastructure of SOCRADES
Architecture for fault-tolerant wireless control
Control under uncertain
wireless sensor and actuator communication
Inclusion in the service- oriented architecture, e.g.
DPWS interface
Demonstrate feasibility of the technology
orate Research - 26
Socrades WP4 will provide
Wireless control architecture
Design methodologies for wireless control algorithms
Event based control ...???
Tools for wireless control loop simulation and design
Based on True Time and Timber, new real time programing approaches
New communication protocols enabling latency control
MAC protocols with support for scheduling and on-line configuration
Lab for wireless control loop tests
ABB AB, Corporate Research - 27
Lab for test of wireless control loops
Future radio environment will interfere with wireless communication
Lab at LTU measuring
Latency
Loss of communication
Microwave owen disturbing a WLAN channel
orate Research - 28
Summary
One standard available – Wireless Hart – other in progress
Equipment are in well defined locations – not ”Ad hoc”
networks
If battery powered requires low power consumption
Significant impact on architecture and communication
Control algorithm needs to be robust against short as well as longer communication outages
Will wireless control need its own frequency band?
