TWO LAYER CONTROL STRATEGY

APPLIED TO BUILDING AUTOMATION

João Figueiredo

Universidade de Évora,CEM-IDMEC, R. Romão Ramalho, 59, 7000 Évora, Portugal

José Sá da Costa

Instituto Superior Técnico, IDMEC, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

Keywords: Distributed Systems, Industrial Networks, SCADA Control and Monitoring.

Abstract: A two level hierarchical control strategy is developed over a network of distributed systems. This paper

shows the great potential of a control strategy over two layers - distributed local controls which are

connected with an intelligent centralized control, which has a global view over the system, and permits an

actualization of the local references, knowing the complete state of the entire system The tested prototype

worked perfectly showing the huge potential of communication systems between distributed processes.

These communication systems allow intelligent centralized algorithms to manage decision making problems

in real-time environments. The system presented in this paper combines several technologies (local PLCs,

SCADA systems and network communications) to reach the goal of efficient management of distributed

processes.

1 INTRODUCTION

Today with the worldwide communications

development it is more and more usual the

decentralized management of systems. This strategy

reaches different fields, from agriculture, to industry,

domotics ... (Christensen, 2002), (Dey, 1999),

(Figueiredo, 2005a).

In the economic field the big companies locate

plants in low-cost lands and research and

commercial activities close to customer

industrialized lands.

In engineering, especially in the industrial field,

the motivation to optimize resources, forces the

communication between decentralized systems in

order to reach better allocation of resources,

minimizing the waste of raw materials, reducing

production costs…

In this context the communication between

distant systems is increasing tremendously, not only

in new built systems but also when reengineering is

brought to old systems. The reengineering of old

plants brings new intelligence to these systems by

introducing automation solutions in their processes.

These new instrumentation systems (intelligent

sensors and actuators) allow the plants to

communicate their actual state to the centralized

control unit, allowing a real-time decision making

(Neto et al., 2004), (Ratinho, 2002).

In this paper an urban application of decentralized

control strategy is presented. A control and

monitoring platform for an Intelligent building is

developed using a SCADA system (Supervisory

Control And Data Acquisition). The control strategy

developed in this paper develops a two-level

architecture where inner-loops are performed by

local PLCs (Programmable Logic Controller), and

the outer-loop is managed by the centralized

SCADA system that interacts with the entire local

PLC network. The outer loop has the potential to

develop a more heavy control algorithm as the

current low-level control actions are managed by the

local PLCs. Tests on a prototype are shown. The

prototype represents a multi-input/output parking

place, composed by several gates distributed by

different building floors, and having a centralized

control unit that manages and monitors the complete

state of the parking place (current number of free

places, gates state, utilization percentage of each

210

Figueiredo J. and Sá da Costa J. (2006).

TWO LAYER CONTROL STRATEGY APPLIED TO BUILDING AUTOMATION.

In Proceedings of the Third International Conference on Informatics in Control, Automation and Robotics, pages 210-216

DOI: 10.5220/0001201802100216

 SciTePress

gate, overall power consumption, fire and smoke

alarms… All the instrumentation in place is

controlled by the industrial PLC network. Each PLC

unit controls a set of sensors and actuators,

responsible for the proper actuation of the input and

output gates located in a multi input-output parking

place.

2 SYSTEM MODEL

The studied building is modeled as tree-structure,

composed by two main sub-structures: Floors and

Rooms (Figueiredo, 2005b).

This structure provides flexibility to the model as

it can deal with both small/simple and big/complex

buildings (Fig. 1). Following this modular model

structure, each room is considered as an autonomous

unit with its independent monitoring and control

activities. The SCADA application is developed

according the model-tree structure presented above,

allowing the user to go down from the general state

view of the entire Building to each floor, descending

continuously to each room and reaching the final

elementary chain devices such as sensors or

actuators.

Figure 1: Intelligent Home as a tree-structure Model.

Each floor is modeled as a set of rooms and each

room has several sensors and actuators.

The set of actuators and sensors considered in

each room are mainly grouped into 2 groups:

- Group A: leaving rooms, bedrooms;

- Group B: kitchens, toilets, parking place.

The set of sensors and actuators considered in

both groups are shown in fig. 2.

An additional feature of this model that provides

the system huge accessibility to their users is the

SCADA platform where this model was

implemented which allows the system to be

connected trough the internet. This feature will be

presented in chapter 3.

Concerning the prototype tested in this paper, the

multi-input multi-output parking place, the

inputs/outputs considered in each gate are illustrated

in fig. 3. Additionally to the specific gate

inputs/outputs showed in fig. 3, there are also, in the

parking place all the sensors/actuators illustrated in

Group B, fig. 2.

Group A: sensors and actuators

Group B: sensors and actuators

Figure 2: Intelligent Home: Sensors and Actuators.

Figure 3: Parking Place Gate inputs/Outputs.

utomatic

System

(SCADA Axeda)

Start

Car In

Car Out

Reset

Master

System

Siemens

S7-300

Slave

System

Siemens

S7-300

Gate 1

PROFIBUS NET

MPI NET

Red

Green

N. In

N. Out

P. Full

INTERNE

Gate n

Start

Car In

Out

Reset

Group A

Lights sensors

Mov. sensors

Light actuators

Alarm actuators

Temp. sensors Air Cond. actuators

Smoke sensors Exhaust actuators

Group B

Lights sensors

Mov. sensors

Light actuators

Alarm actuators

Temp. sensors Air Cond. actuators

Smoke sensors Exhaust actuators

Water sensors

Gas sensors

Central Water supply

Central Gas supply

TWO LAYER CONTROL STRATEGY APPLIED TO BUILDING AUTOMATION

211

3 MONITORING AND CONTROL

STRATEGY

3.1 Control Strategy

The strategy developed in this paper is commonly

known as a two-level hierarchical control model as it

integrates a first control loop that is managed by

local PLCs with a second loop which is performed

by a SCADA supervisory system that monitors

globally the several distributed local systems

(Figueiredo, 2005b). Figures 4 and 5 illustrate this

control strategy: The inner control (first loop) and

the outer control loop.

Figure 4: First Loop Control – PLC Local Control.

Figure 5: Second Loop Control – SCADA Supervisor

Control.

Applying this strategy to a complex building that

is instrumented and monitored through a SCADA

supervisory system, we can manage globally the

entire net of field PLCs that control locally each own

process.

The upper level control law, having a global

system overview, generates the set of references for

each local process (PLC) avoiding possible conflicts

in emergency situations. The input functions for the

upper control loop are mentioned as comfort laws,

safety laws (F1(t), … ,Fj(t)).

3.2 PLC Network and SCADA

Supervisor

The developed strategy to cope with complex

buildings with a huge set of geographically

distributed actuators and sensors is implemented

through a PLC network (fig. 6) consisting of several

slaves PLCs connected to a master PLC via

Profibus/ DP network.

Each slave PLC hosts several control programs

which selection is made either locally, via an HMI

(Human Machine Interface) or remotely, via the

master PLC (PLC 0), which is connected to the

server PC, via RS232/ MPI Siemens protocol, where

the SCADA application is running.

The server PC is simultaneous a SCADA server

and an internet server, as the implemented SCADA

application is web enabled. All process variables are

available at the SCADA PC as these variables are

on-line available through the Profibus/ DP Master-

Slave network.

Figure 6: PLC Network and SCADA supervisor.

PLC

Ref 1.1

Ref 1.2

Ref 1.n

q 1.n

q 1.2

q 1.1

PLC

Ref 1.i

q 1.i

PLC

Ref k.i

q k.i

q 1.i q k.i

(

)

SCADA Su

erviso

Ref 1.i

Ref k.i

ICINCO 2006 - ROBOTICS AND AUTOMATION

212

3.3 SCADA Supervisory Control

Loop

System Description: The SCADA system used to

implement this monitoring and control strategy was

a commercial platform: Axeda Supervisor Wizcon

for Windows & Internet V 8.2.

The Driver used in this application to establish the

communication Scada system – Master-PLC was the

Siemens RS232/MPI interface, via the Siemens

software Simatic S7 Prodave. According to this

communication Protocol, a PLC digital variable

address must be defined as NNTXAAAABB, where:

NN = PLC address (from 0 to 32);

T = memory area type (I for Input, Q for

Output and M for memory);

X = variable type (B for Byte, W for Word);

AAAA = slot address (from 0000 to 9999);

BB = variable address (00 to 17).

In the specific case of the prototype tested in this

paper, it is necessary to exchange integer values

between the several local PLCs in order to update

the system overall capacity (actual number of free

places in the park).

The SCADA system receives continuously the

information from all PLCs in the network through

the master-PLC and calculates the number of free

places available in the parking place. This integer

values is on-line updated to the PLC network and

according this value the corresponding state of the

entrance lights (red/ green) is determined. When the

number of free places equals zero, the entrance red

lights in all the park gates are set on, until a car exits

the park. This car exit can take place from one of the

several available gates in the parking place.

The transfer of integer values between the

SCADA system, the master-PLC, and forward, to all

slave-PLCs, it is possible through Data Base

transfer. According to the MPI protocol, an integer

value to be transferred from the PLC to the SCADA

system and vice versa, it must be addressed as

NNTXDDDAAAA, where:

NN = PLC address (from 0 to 32);

T = memory area type (D for Data Block, I

for Input, Q for Output and M for

memory);

X = variable type (B for Byte, W for Word);

DDD = Data Block identification (from 000 to

999);

AAAA = variable byte address in Data Block.

Among the main functionalities of a SCADA

system there is the so called “Tag”. A “Tag” is a

defined variable that permits the exchange of

information between the PLC network and the

SCADA system, in a real-time environment. There

are usually three types of Tags: PLC, Dummy and

Compound. In the PLC Tags the PLC sets the

variable values that are directly transferred to the

Scada program. In the Dummy Tags the value is set

by the user on the Scada interface and transferred to

the PLC address. Finally Compound Tags are set by

the Scada program, following the programmed

operations.

When defining the Tags a set of information is

required, namely: Tag name, Description, Tag

source, Driver, Sample rate, Address and Tag Type.

An example of such Tag definition is illustrated in

Fig. 7.

Figure 7: Tag definition.

The Scada main interface between the system and

the user are the application images. The image

building is a functionality of all SCADA systems

and its main function is to permit the user a quick

visual identification of all system functional

characteristics. An easy identification of the system

Inputs and Outputs permits the user an effective

monitoring and a quick actuation on the process,

when it is necessary.

The developed application used important

features that we named animated images. These

images change geometry characteristics and colours

when their digital variables change the state (on/

off).

TWO LAYER CONTROL STRATEGY APPLIED TO BUILDING AUTOMATION

213

3.4 PLC Master-Slave Network

System Description: The PLCs used to implement

the local control strategy were the Siemens S7-3**.

The Siemens software used to implement the

PLC application was the Simatic Manager. The

program language used was the Ladder Diagram

(LAD).

A PLC master-slave network was established

through a Profibus protocol (Siemens, 2001).

The main characteristics of the PLC master-slave

network implemented in the prototype is shown in

fig 8. In fig. 9 the overall PLC network implemented

in this paper is presented.

Figure 8: Main characteristics of PLC Master-Slave

network.

Figure 9: Profibus Master-Slave network.

Local Control Strategy: At the local control level,

several algorithms have been developed for the

intelligent building: Property Violation, Temperature

control, Gas and Water leakages, parking gate

management…

Using the Grafcet methodology, the main

characteristics developed for the parking gate

management is presented below (fig. 10).

The input variables referred in fig. 10 represent:

Out = binary sensor indicating a vehicle that

wants to exit the park;

IN = binary sensor indicating a vehicle that

wants to enter in the park;

Free Place = integer value representing the

actual free places available in the park,

at each time.

The output variables referred in fig. 10

represent:

Green = Green light at the parking gate;

Red = Red light at the parking gate;

Gate = Gate actuator that closes and opens the

parking gate;

FP = Function Block that calculates the

actual Free Places in the Park. This

Function Block is associated with a

Data Base Block, which is accessed by

all PLCs connected in the PROFIBUS

network.

Figure 10: Grafcet for Parking gate management.

Together with this gate management system,

there are also other automatic systems running in the

local PLCs: property violation control, temperature

control…

3 4

OUT

Gate = ON

Call FP

Green = ON

Red = OFF

Start

Green = ON

Red = OFF

Gate = OFF

FP = max.

Call FP

Gate = ON

Call FP

Start. IN. FP = max

Gate = ON

Call FP

OUT. Free Place > 0 IN. Free Place > 0

Red = ON

Green = OFF

Gate = OFF

Free Place = 0

* * **

Reset

ICINCO 2006 - ROBOTICS AND AUTOMATION

214

4 EXPERIMENTAL SETUP

The developed application to monitor and control

intelligent buildings has been implemented in an

experimental setup to control a parking place with

multiple distributed entrances/exits.

The prototype developed has the following

software and hardware requirements.

4.1 Software Requirements

The Scada system was developed over the platform

Axeda Supervisor Wizcon for Windows & Internet

V8.2.

Siemens Simatic Manager V5.2 and Siemens

Simatic S7 Prodave V5.5 were used to program the

PLCs and to establish communication between the

Scada system and the Master-PLC, respectively.

The Siemens NCM S7 for Profibus was used to

configure the Profibus Master-Slave PLC network.

(Siemens, 2001)

4.2 Hardware Requirements

The PLC network implemented had two PLCs

Siemens S7-3** (one PLC controlling each gate).

The PLC which controls the gate 1 was set as the

master PLC and it was connected to the Scada

System via the Siemens RS232/MPI protocol.

The gate sensors and actuators were simulated

through the FESTO interface SYSLINK (fig. 11).

4.3 Experimental Results

Developed Application Menus:

Several Scada menus had been built. The main

characteristic of a Scada Menu is to be simple,

explicit and quick on transmitting the information to

the system operator. The first Menu developed is a

general overview Menu, named “Main Menu” which

gives us access to the several sections of the

intelligent house and permits the operator to leave

the Scada control and monitoring application (fig.

12). Climbing the tree structure from the main menu

we can reach anyone of the floors that compose the

house. In Fig. 13, the parking place is shown. This

Menu informs about the number of vehicles that

entered or left the park at each gate and the number

of actual free places in the park. Additionally it

shows the state of all sensors and actuators in the

parking place (lights, smoke, gas, water…). From

this Menu we can return to the main Menu, or to

jump into the overview menu.

Specially referring the sensors: lights, water and

gas leakages, the programmed animated images

characterize the binary sensor states by a change of

colour: green indicates the sensor is activated and

red indicates the sensor is inactive.

Concerning the property violation system, this

application developed an alarm that actuates when

the corresponding sensors are actuated (in fig. 13,

sensors s16 and s26 are movement sensors).

Figure 11: Experimental Setup for gate management.

Figure 12: Scada: Main Menu.

TWO LAYER CONTROL STRATEGY APPLIED TO BUILDING AUTOMATION

215

Figure 13: Scada: Parking place menu.

The park overview menu is shown in fig. 14. It

gives the system operator a quick overview over the

parking place capacity (number of cars that entered

or left the park at each gate, actual number of free

places, gates state…)

Figure 14: Scada: Park Overview Menu.

5 CONCLUSIONS

This paper shows the great potential of a control

strategy over two lawyers - distributed local controls

which are connected with an intelligent centralized

control, which has a global view over the system,

and permits an actualization of the local references,

knowing the complete state of the entire system.

The tested prototype worked perfectly showing

the huge potential of communication systems

between distributed processes. These

communication systems allow intelligent centralized

algorithms to manage decision making problems in

real-time environments. The system presented in this

paper combines several technologies (local PLCs,

SCADA systems and network communications) to

reach the goal of efficient management of distributed

processes.

REFERENCES

Christensen, H. (2002). Domestic Robots. Proc. 2002 10

IEEE Mediterranean Conf. On Control and

Automation – MED2002, Lisbon, Portugal.

Dey, A., G. Abowd, D. Salber. (1999) A Context-based

Infrastructure for Smart Environments, Managing

Interactions in Smart Environments. Springer-

Verlag, pp. 114-130.

Figueiredo, J., M. Botto. (2005). Automatic Control

Strategies Implemented on a Water Canal Prototype.

Proc. 16

IFAC World Congress – Intl. Federation of

Automatic Control, Praha, Czech Republic.

Figueiredo, J., J. M. Sá Costa. (2005). A Two Level

Hierarchical Control Strategy Applied to an Intelligent

House. Proc. IEEE Intl. Symp. On Intelligent Signal

Processing, Faro, Portugal.

Neto, A., J. Martins, S. Zolnier, P. Monteiro, F. Baeta.

(2004). 1-Wire ™ System Performance – An

Application for Temperature Measurement in

Agricultural Buildings. Proc. 2004 6

Conf. On

Automatic Control – CONTROLO 2004, Faro,

Portugal, pp. 445-450.

Orr, R., G. Abowd. (2001). The smart Floor: A

Mechanism for Natural User Identification and

Tracking. Proc. 2001 Intl. Conf. On Human Factors in

Computing Systems, Netherlands.

Ratinho, T., J. Figueiredo, M. Rijo. (2002). Modelling,

Control and Field Tests on an Experimental Irrigation

Canal. Proc. 2002 10

IEEE Mediterranean Conf. On

Control and Automation – MED2002, Lisbon,

Portugal.

Siemens. (2001). Simatic Net – NCM S7 for Profibus/

FMS. Siemens 12/2001

ICINCO 2006 - ROBOTICS AND AUTOMATION

216