1. INDUSTRIAL AUTOMATION

1.1 AUTOMATION Automation is basically the delegation of human control functions to technical equipment aimed towards achieving:Higher productivitySuperior quality of end productEfficient usage of energy and raw materialsImproved safety in working conditions etc.

1.2 TYPES OF AUTOMATIONBuilding automationExample: lifts, smoke detectorsOffice automationExample: printers, cctv camerasScientific automationExample: rocket launchingLight automationExample: street solar lightingIndustrial automation Example: automated bottle filling stations, steel factories

1.3 TOOLS OF AUTOMATION Programmable logic controller (PLC) Supervisory Control And Data Acquisition (SCADA) Human Machine Interface (HMI) or Touch Screen (TS) Variable Frequency Drive (VFD)1.4 HISTORY OF AUTOMATION Manual control Pneumatic control Hard wired logic control Electronic control using logic gates Programmable logic controllerMANUAL CONTROL: All the actions related to process control are taken by the operatorsDrawbacks: Likely human errors and consequently its effect on quality of final product The production, safety, energy consumption and usage of raw material are all subject to the correctness and accuracy of human action.PNEUMATIC CONTROL: Industrial automation with its machine and process control, had its origin in the 1920s with the advent of Pneumatic Controllers Actions were controlled by a simple manipulation of pneumatic valves, which in turn were controlled by relays and switches.Drawbacks: Bulky and complex system Involves lot of rework to implement control logic Longer project timeHARD WIRED LOGIC CONTROL: The contactor and relays together with hardware timer and counters were used in achieving the desired level of automationDrawbacks: Bulky panels Complex wiring Longer project time Difficult maintenance and troubleshootingELECTRONIC CONTROL USING LOGIC GATES: In 1960s with the advent of electronics, the logic gates started replacing the relays and auxiliary contactors in the control circuits The hardware timers& counters were replaced by electronic timersAdvantages: Reduced space requirement Energy saving Less maintenance & greater reliabilityDrawbacks: Change in control logic not possible More project time

Programmable Logic Controller : In 1970s with the coming of microprocessors and associated peripheral chips, the whole process of control and automation underwent a radical change Instead of achieving the desired control or automation through physical wiring of control devices, in PLC it is achieved through a program or say software The programmable controllers have in recent years experienced an unprecedented growth as universal element in industrial automation. It can be effectively used in applications ranging from simple control like replacing small number of relays to complex automation problems

AUTOMATION TOOLS

ANN Artificial Neural NetworkDCS Distributed Control SystemHMI Human Machine InterfaceSCADA Supervisory Control and Data AcquisitionPLC Programmable Logic ControllerInstrumentationMotion ControlRobotics

1.5 IMPACT OF AUTOMATION

Automation has had a notable impact in a wide range of highly visible industries beyond manufacturing. Once-ubiquitous telephone operators have been replaced largely by automated telephone switchboards and answering machines Medical processes such as primary screening in electrocardiography or radiography and laboratory analysis of human genes, cells, and tissues are carried out at much greater speed and accuracy by automated systems. In general, automation has been responsible for the shift in the world economy from agrarian in the 19th century and from industrial to services in the 20th century1.6 Industrial Automation vs. Industrial Information Technology:However, Industrial Automation is distinct from IT in the following senses A. Industrial Automation also involves significant amount of hardware technologies, related to Instrumentation and Sensing, Actuation and Drives, Electronics for Signal Conditioning, Communication and Display, Embedded as well as Stand-alone Computing Systems etc. B. As Industrial Automation systems grow more sophisticated in terms of the knowledge and algorithms they use, as they encompass larger areas of operation comprising several units or the whole of a factory, or even several of them, and as they integrate manufacturing with other areas of business, such as, sales and customer care, finance and the entire supply chain of the business, the usage of IT increases dramatically. However, the lower level Automation Systems that only deal with individual or , at best, a group of machines, make less use of IT and more of hardware, electronics and embedded computingTypes of Automation Systems Automation systems can be categorized based on the flexibility and level of integration in manufacturing process operations. Various automation systems can be classified as follows Fixed Automation: It is used in high volume production with dedicated equipment, which has a fixed set of operation and designed to be efficient for this set. Continuous flow and Discrete Mass Production systems use this automation. e.g. Distillation Process, Conveyors, Paint Shops, Transfer lines etc. A process using mechanized machinery to perform fixed and repetitive operations in order to produce a high volume of similar parts. Programmable Automation: It is used for a changeable sequence of operation and configuration of the machines using electronic controls. However, non-trivial programming effort may be needed to reprogram the machine or sequence of operations. Investment on programmable equipment is less, as production process is not changed frequently. It is typically used in Batch process where job variety is low and product volume is medium to high, and sometimes in mass production also. e.g. in Steel Rolling Mills, Paper Mills etc. Flexible Automation: It is used in Flexible Manufacturing Systems (FMS) which is invariably computer controlled. Human operators give high-level commands in the form of codes entered into computer identifying product and its location in the sequence and the lower level changes are done automatically. Each production machine receives settings/instructions from computer. This automatically loads/unloads required tools and carries out their processing instructions. After processing, products are automatically transferred to next machine. It is typically used in job shops and batch processes where Version 2 EE IIT, Kharagpur 11 product varieties are high and job volumes are medium to low. Such systems typically use Multipurpose CNC machines, Automated Guided Vehicles (AGV) etc. Integrated Automation: It denotes complete automation of a manufacturing plant, with all processes functioning under computer control and under coordination through digital information processing. It includes technologies such as computer-aided design and manufacturing, computer-aided process planning, computer numerical control machine tools, flexible machining systems, automated storage and retrieval systems, automated material handling systems such as robots and automated cranes and conveyors, computerized scheduling and production control. It may also integrate a business system through a common database. In other words, it symbolizes full integration of process and management operations using information and communication technologies. Typical examples of such technologies are seen in Advanced Process Automation Systems and Computer Integrated Manufacturing (CIM)

1.7 ADVANTAGES: Accurate and consistent information Faster fault identification Improved availability of system Increased production Reduced cost Maintenance of quality and quantity Improved safety conditions

PLC Programmable Logic Controller

2.1 INTRODUCTION TO PLC"A digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions by implementing specific functions such as logic sequencing, timing, counting, and arithmetic to control, through digital or analog input/output modules, various types of machines or processes. The digital computer which is used to perform the functions of a programmable controller is considered to be within this scope. Excluded are drum and other similar mechanical sequencing controllers." A programmable logic controller (PLC) is a special purpose computer aimed at implementing control solutions. Historically PLCs have been used mainly for on-off or logic type applications. However, modern PLCs have become increasingly sophisticated and can now cover quite complex control tasks

2.2 HISTORY OF PLC When the first electronic machine controls were designed, they used relays to control the machine logic (i.e. press "Start" to start the machine and press "Stop" to stop the machine). A basic machine might need a wall covered in relays to control all of its functions. There are a few limitations to this type of control. Relays fail. The delay when the relay turns on/off. There is an entire wall of relays to design/wire/troubleshoot. A PLC overcomes these limitations; it is a machine controlled operation. Recent developments PLCs are becoming more and more intelligent. In recent years PLCs have been integrated into electrical communications (Computer network)i.e., all the PLCs in an industrial environment have been plugged into a network which is usually hierarchically organized. The PLCs are then supervised by a control centre. There exist many proprietary types of networks. One type which is widely known is SCADA (Supervisory Control and Data Acquisition).

2.3 PLC ARCHITECTURE

This Systems and processes requiring "on/off" control abound in modern commerce and industry, but such control systems are rarely built from either electromechanical relays or discreet logic gates. Instead, digital computers fill the need, which may be programmed to do a variety of logical functions. The purpose of a PLC was to directly replace electromechanical relays as logic elements, substituting instead a solid-state digital computer with a stored program, able to emulate the interconnection of many relays to perform certain logical tasks.

2.4 PLC COMPONENTSA Programmable Logic Controller, PLC or Programmable Controller is a digital computer used for automation of electromechanical processes. The Programmable Logic Controller (PLC) is basically a computer. Even the smallest PLC has a microprocessor, which qualifies it as a computer

PLCs are used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. A PLC has many "input" terminals, through which it interprets "high" and "low" logical states from sensors and switches. It also has many output terminals, through which it outputs "high" and "low" signals to power lights, solenoids, contactors, small motors, and other devices lending themselves to on/off control. In an effort to make PLCs easy to program, their programming language was designed to resemble ladder logic diagrams. Thus, an industrial electrician or electrical engineer accustomed to reading ladder logic schematics would feel comfortable programming a PLC to perform the same control functions.

Supervisory Control and Data Acquisition (SCADA)

3.1 INTRODUCTION TO SCADASCADA Overview SCADA is an acronym for Supervisory Control and Data Acquisition. SCADA systems are used to monitor and control a plant or equipment in industries such as telecommunications, water and waste control, energy, oil and gas refining and transportation. These systems encompass the transfer of data between a SCADA central host computer and a number of Remote Terminal Units (RTUs) and/or Programmable Logic Controllers (PLCs), and the central host and the operator terminals. A SCADA system gathers information (such as where a leak on a pipeline has occurred), transfers the information back to a central site, then alerts the home station that a leak has occurred, carrying out necessary analysis and control, such as determining if the leak is critical, and displaying the information in a logical and organized fashion. These systems can be relatively simple, such as one that monitors environmental conditions of a small office building, or very complex, such as a system that monitors all the activity in a nuclear power plant or the activity of a municipal water system. Traditionally, SCADA systems have made use of the Public Switched Network (PSN) for monitoring purposes. Today many systems are monitored using the infrastructure of the corporate Local Area Network (LAN)/Wide Area Network (WAN). Wireless technologies are now being widely deployed for purposes of monitoring.

SCADA processes include industrial, infrastructure, and facility-based processes, as described below: Industrial processes include those of manufacturing, production, power generation, fabrication, and refining, and may run in continuous, batch, repetitive, or discrete modes. Infrastructure processes may be public or private, and include water treatment and distribution, wastewater collection and treatment, oil and gas pipelines, electrical power transmission and distribution, wind farms, civil defense siren systems, and large communication systems. Facility processes occur both in public facilities and private ones, including buildings, airports, ships, and space stations. They monitor and control heating, ventilation, and air conditioning systems (HVAC), access, and energy consumption.SCADA systems consist of: One or more field data interface devices, usually RTUs, or PLCs, which interface to field sensing devices and local control switchboxes and valve actuators A communications system used to transfer data between field data interface devices and control units and the computers in the SCADA central host. The system can be radio, telephone, cable, satellite, etc., or any combination of these. A central host computer server or servers (sometimes called a SCADA Center, master station, or Master Terminal Unit (MTU) A collection of standard and/or custom software [sometimes called Human Machine Interface (HMI) software or Man Machine Interface (MMI) software] systems used to provide the SCADA central host and operator terminal application, support the communications system, and monitor and control remotely located field data interface devices

3.2 SCADA SYSTEM AND ITS FUNCTIONS SCADA is a means of controlling from remote location by using communication technology. It is used to collect data and control processes at the supervisory level. The SCADA monitored system could be just about an oil refinery plant, a power generation system, a communication network or even a simple switch. To monitor and control the automation system, the SCADA collects data from the system and issue commands accordingly. By using sensors (discrete or analog) and control relays, the SCADA collects information about processes and control individual equipment. The system is supervised by a SCADA master station which collects data from monitoring devices and issues controls accordingly (either automatically or at the request of human operators) . The SCADA system comprises of, 1. Sensors (either digital or analog): Sensors control relays that directly interface with the managed system. 2. Remote telemetry units (RTU): These are small computerized units deployed in the field at specific sites and locations. It serves as local collection points for gathering information from sensors and delivering commands to control relays. 3. Communications network: It connects the SCADA master station to the RTU. 4. SCADA master units: These are larger computer consoles that serve as the central processor for the SCADA system. Master units provide a human interface to the system and automatically regulate the managed system in response to sensor inputs.

3.3 DISADVANTAGES OF RELAYS Relays used only for on/off control. Complicated control systems Expensive System. System takes up much floor and space. Control relays are power- hungry, heat generation. Any change in control program requires the rewiring of relays. For complicated control systems, it is difficult to troubleshoot and locate the faults.

3.4 ADVANTAGES OF SCADA SYSTEM Easily programmed or reprogrammed Easy maintained (self diagnostic). Capability to do arithmetic function. The ability to communicate with other controller or a master host computer. PLCs. were able to move past simple on/off control to more complex schemes as PID control.

3.5 Benefits of Implementing SCADA systems for Electrical Distribution: Increases reliability through automation Eliminates the need for manual data collection Alarms and system-wide monitoring enable operators to quickly spot and address problems Automation protects workers by enabling problem areas to be detected and addressed automatically Operators can use powerful trending capabilities to detect future problems, provide better routine maintenance of equipment and spot areas for improvement Historians provides the ability to view data in various ways to improve efficiency

A SCADA system performs four functions: 1. Data acquisition 2. Networked data communication 3. Data presentation 4. ControlThese functions are performed by four kinds of SCADA components: 1. Sensors (either digital or analogue) and control relays that directly interface with the managed system. 2. Remote telemetry units (RTUs). These are small computerized units deployed in the field at specific sites and locations. RTUs serve as local collection points for gathering reports from sensors and delivering commands to control relays. 3. SCADA master units. These are larger computer consoles that serve as the central processor for the SCADA system. Master units provide a human interface to the system and automatically regulate the managed system in response to sensor inputs. 4. The communications network that connects the SCADA master unit to the RTUs in the field. Data Acquisition SCADA system needs to monitor hundreds or thousands of sensors. Sensors measure: 1. Inputs and outputs e.g. water flowing into a reservoir (input), valve pressure as water is released from the reservoir (output).2. Discrete inputs (or digital input) e.g. whether equipment is on or off, or tripwire alarms, like a power failure at a critical facility. 3. Analogue inputs: where exact measurement is important e.g. to detect continuous changes in a voltage or current input, to track fluid levels in tanks, voltage levels in batteries, temperature and other factors that can be measured in a continuous range of input. For most analogue factors, there is a normal range defined by a bottom and top level e.g. temperature in a server room between 15 and 25 degrees Centigrade. If the temperature goes outside this range, it will trigger a threshold alarm. In more advanced systems, there are four threshold alarms for analogue sensors, defining Major Under, Minor Under, Minor Over and Major Over alarms.3.6 ELEMENTS OF SCADA: Sensor and actuators RTUs and PLCs Communication MTU Front end processor SCADA server Historical/redundant/safety server HMI computer HMI software

SENSORSTypes of sensors: Pressure sensors Temperature sensors Light sensors Humidity sensors Wind speed sensors Water level sensors Distance sensorsACTUATORS Valve Pumps MotorsRTUs (Remote Terminal Unit) Intelligent to control a process and multiple processe Data logging and alarm handling Expandable Asks the field devices for information Can control IEDs (intelligent electronic device) Slave/master deviceSCADA SERVER It can be a web server Data logging Analyzing data Serve the clients through a firewall Clients connected in the corporation or connected outside through internet Real-time decision maker Asks RTU for information

First generation: "Monolithic Early SCADA system computing was done by large minicomputers. Common network services did not exist at the time SCADA was developed. Thus SCADA systems were independent systems with no connectivity to other systems. The communication protocols used were strictly proprietary at that time. The first-generation SCADA system redundancy was achieved using a back-up mainframe system connected to all the Remote Terminal Unit sites and was used in the event of failure of the primary mainframe system. Some first generation SCADA systems were developed as "turn key" operations that ran on minicomputers such as the PDP-11 series made by the Digital Equipment CorporationSecond generation: "DistributedSCADA information and command processing was distributed across multiple stations which were connected through a LAN. Information was shared in near real time. Each station was responsible for a particular task thus making the size and cost of each station less than the one used in First Generation. The network protocols used were still not standardized. Since the protocols were proprietary, very few people beyond the developers knew enough to determine how secure a SCADA installation was. Security of the SCADA installation was usually overlooked.Third generation: "Networked Similar to a distributed architecture, any complex SCADA can be reduced to simplest components and connected through communication protocols. In the case of a networked design, the system may be spread across more than one LAN network and separated geographically. Several distributed architecture SCADAs running in parallel, with a single supervisor and historian, could be considered a network architecture. This allows for a more cost effective solution in very large scale systems.Fourth generation: "Internet of Things With the commercial availability of cloud computing, SCADA systems have increasingly adopted Internet of Things technology to significantly reduce infrastructure costs and increase ease of maintenance and integration. As a result SCADA systems can now report state in near real-time and use the horizontal scale available in cloud environments to implement more complex control algorithms than are practically feasible to implement on traditional programmable logic controllers. Further, the use of open network protocols such as TLS inherent in Internet of Things technology provides a more readily comprehendible and manageable security boundary than the heterogeneous mix of proprietary network protocols typical of many decentralized SCADA implementations.3.7 BENEFITS OF PLC-SCADA PLC and SCADA are the success behind the automation industry. PLC is designed in such a way that it can be used to control multiple inputs and outputs and it can be handled in extreme temperature changes. Without these two automation concepts the automation industry fails. So there is a huge demand for skilled manpower in PLC and SCADA in automation industry. We cannot even think of surviving without this technology even for a day. If the system fails then there would be losses of cores of rupees. After the application of PLC and SCADA technology in Industrial automation process. It is creating a lot of employment opportunities There is a huge demand for skilled manpower in this sector Reduces time Reduces Cost Profit maximization Economies of scale Improved Productivity Quality output Increased Accuracy and speed

HMI Human Machine Interface4.1 INTRODUCTION TO HMITo work with a system, users have to be able to control and assess the state of the system. For example, when driving an automobile, the driver uses the steering wheel to control the direction of the vehicle, and the accelerator pedal, brake pedal and gearstick to control the speed of the vehicle. The driver perceives the position of the vehicle by looking through the windshield and exact speed of the vehicle by reading the speedometer. The user interface of the automobile is on the whole composed of the instruments the driver can use to accomplish the tasks of driving and maintaining the automobile.There is a distinct difference between User Interface versus Operator Interface or Human Machine Interface (HMI). The term user interface is often used in the context of (personal) computer systems and electronic devices Where a network of equipment or computers is interlinked through an MES (Manufacturing Execution System)-or Host. An HMI is typically local to one machine or piece of equipment, and is the interface method between the human and the equipment/machine. An Operator interface is the interface method by which multiple equipment that are linked by a host control system is accessed or controlled. The system may expose several user interfaces to serve different kinds of users. For example, a computerized library database might provide two user interfaces, one for library patrons (limited set of functions, optimized for ease of use) and the other for library personnel (wide set of functions, optimized for efficiency).The user interface of a mechanical system, a vehicle or an industrial installation is sometimes referred to as the human- machine interface (HMI). HMI is a modification of the original term MMI (man-machine interface). In practice, the abbreviation MMI is still frequently used although some may claim that MMI stands for something different now. Another abbreviation is HCI, but is more commonly used for than human-computer interface. Other terms used are operator interface console (OIC) and operator interface terminal (OIT). However it is abbreviated, the terms refer to the 'layer' that separates a human that is operating a machine from the machine itself. In science fiction, HMI is sometimes used to refer to what is better described as direct neural interface. However, this latter usage is seeing increasing application in the real-life use of (medical) prosthesesthe artificial extension that replaces a missing body part (e.g., cochlear implants). In some circumstance computers might observe the user, and react according to their actions without specific commands. A means of tracking parts of the body is required, and sensors noting the position of the head, direction of gaze and so on have been used experimentally. This is particularly relevant to immersive interfaces.

A basic goal of HMI is to improve the interactions between users and machines (computers) by making computers more usable and receptive to the user's needs. Specifically, HMI is concerned with: methodologies and processes for designing interfaces (i.e., given a task and a class of users, design the best possible interface within given constraints, optimizing for a desired property such as learning ability or efficiency of use) methods for implementing interfaces (e.g. software toolkits and libraries; efficient algorithms) techniques for evaluating and comparing interfaces developing new interfaces and interaction techniques developing descriptive and predictive models and theories of interaction A long term goal of HMI is to design systems that minimize the barrier between the human's cognitive model of what they want to accomplish and the computer's understanding of the user's task. Professional practitioners in HMI are usually designers concerned with the practical application of design methodologies to real-world problems. Their work often revolves around designing graphical user interfaces and web interfaces. Researchers in HMI are interested in developing new design methodologies, experimenting with new hardware devices, prototyping new software systems, exploring new paradigms for interaction, and developing models and theories of interaction.4.2 ADVANTAGES OF HMIHigh quality graphics for realistic representations of machinery and processesThis will give the operator and the management a very realistic view of the plant. The operator can control plant without in one central location, this could be very useful when there is a security concerns. The operator does not need to be close to the equipment to control of monitor.

Alarms (Real Time / Historical)Viewing alarms will help the operator to locate and react faster to any malfunction of any anomalies. Some of the alarms could be of preventive type, for example to create a warning alarm on a hydraulic tank oil level before the oil level really reaches a critical point.Historical Alarm logging is very useful to track problems. It could be used to optimize process. Which in turn would increase productivity and reduce lost time?Trends (Real Time / Historical)Trends are very useful with PID's. You can view the curve used to reach a certain set point. Study of certain values will result in optimizing your process, and it will certainly make if much more efficient.Recipe ManagerSimple and complex recipe could be controlled with HMI. This is very useful and very effective way to execute recipes.SimulationSome of the high quality HMI's will be so flexible that you can simulate a plant in your office. This will help PLC program developers test their program without having a single equipment or devices. This kind of simulation is used more and more to reduce startup time.MessagingThis is a very interesting functionality. You can message, page or fax someone when a certain event happens. For example lets say the oil level in the hydraulic tank has reaching a low level. Then low oil level will be triggered and it will page the person in charge to fill up the tank.Animate equipments and instrument based on operator standards.They say one picture is better than 100 words. Now this is not only a picture it is an animated one. This will really improve the whole view of the process. Any anomalies will be detected much easier.Reduce the cost of hardware.An HMI can replace hundreds of Push buttons, selectors, Lights and so on. As a result less consoles and panels and definitely less cables all over the plant.CommunicationToday most HMI's can communicate with many different brands of PLC's. Here is a list of most used communications.

DCS Distributed Control System

5.1 INTRODUCTION TO DCSAdistributed control system(DCS) is acontrol systemfor a process or plant, wherein control elements are distributed throughout the system. This is in contrast to non-distributed systems, which use a single controller at a central location. In a DCS, a hierarchy of controllers is connected by communications networks for command and monitoring.Example scenarios where a DCS might be used include: Chemical plants Petrochemical (oil) and refineries Pulp and Paper Mills Boiler controls and power plant systems Nuclear power plants Environmental control systems Water management systems Metallurgicalprocess plants Pharmaceutical manufacturing Sugar refining plants Dry cargo and bulk oil carrier ships Formation control of multi-agent systemsA DCS typically uses custom designed processors as controllers and uses both proprietary interconnections and standard communications protocol for communication. Input and output modules form component parts of the DCS. The processor receives information from input modules and sends information to output modules. The input modules receive information from input instruments in the process (or field) and the output modules transmit instructions to the output instruments in the field. The inputs and outputs can be either analogwhich are continuously changing or discrete signals which are 2 state either on or off. Computer buses or electrical buses connect the processor and modules through multiplexer or demultiplexers. Buses also connect the distributed controllers with the central controller and finally to theHumanmachine interface(HMI) or control consoles.

5.2 DEVELOPMENTS IN DCSThe latest developments in DCS include the following new technologies:1. Wirelesssystems and protocols2. Remote transmission, logging and data historian3. Mobile interfacesand controls4. Embedded web-serversIncreasingly, and ironically, DCS are becoming centralized at plant level, with the ability to log in to remote equipment. This enables the provision of a superiorhuman-machine interface(HMI) especially from the point of view of remote access andportability.As wireless protocols are developed and refined, DCS increasingly includes wireless communication. DCS controllers are now often equipped with embedded servers and provide on-the-go web access.Many vendors provide the option of a mobile HMI, ready for bothAndroidandiOS. With these interfaces, the threat of security breaches and possible damage to plant and process are now very real.

Variable Frequency Drive (VFD)

Avariable-frequency drive(VFD) (also termedadjustable-frequency drive,variable-speed drive,AC drive,micro driveor inverterdrive) is a type ofadjustable-speed driveused inelectro-mechanicaldrive systems to controlAC motorspeedand torqueby varying motor inputfrequencyandvoltage. VFDs are used in applications ranging from small appliances to the largest of mine mill drives and compressors. However, around 25% of the world's electrical energy is consumed by electric motors in industrial applications, which are especially conducive for energy savings using VFDs in centrifugal load service,and VFDs' globalmarket penetrationfor all applications is still relatively small. That lack of penetration highlights significant energy efficiency improvement opportunities for retrofitted and new VFD installations.Over the last four decades,power electronicstechnology has reduced VFD cost and size and has improved performance through advances in semiconductor switching devices, drive topologies, simulation and control techniques, and control hardware and software.VFDs are available in a number of different low- and medium-voltageAC-ACand DC-AC topologies

A variable-frequency drive is a device used in a drive system consisting of the following three main sub-systems: AC motor, main drivecontrollerassembly, and drive/operator interface.AC MotorThe AC electric motor used in a VFD system is usually athree-phaseinduction motor. Some types ofsingle-phasemotors can be used, but three-phase motors are usually preferred. Various types ofsynchronous motorsoffer advantages in some situations, but three-phase induction motors are suitable for most purposes and are generally the most economical motor choice. Motors that are designed for fixed-speed operation are often used. Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 ofNEMAStandard MG-1. ControllerThe VFD controller is asolid-statepower electronics conversion system consisting of three distinct sub-systems: arectifierbridge converter, adirect current(DC) link, and an inverter.Voltage-sourceinverter (VSI) drives (see 'Generic topologies' sub-section below) are by far the most common type of drives. Most drives areAC-ACdrives in that they convert AC line input to AC inverter output. However, in some applications such as common DC bus orsolarapplications, drives are configured as DC-AC drives. The most basic rectifier converter for the VSI drive is configured as a three-phase, six-pulse,full-wavediode bridge. In a VSI drive, the DC link consists of acapacitorwhich smoothes out the converter's DC outputrippleand provides a stiff input to the inverter. This filtered DC voltage is converted to quasi-sinusoidalAC voltage output using the inverter's active switching elements. VSI drives provide higherpower factorand lowerharmonic distortionthanphase-controlledcurrent-sourceinverter (CSI) and load-commutated inverter (LCI) drives (see 'Generic topologies' sub-section below). The drive controller can also be configured as aphase converterhaving single-phase converter input and three-phase inverter output.

Controller advances have exploited dramatic increases in the voltage and current ratings and switching frequency of solid-state power devices over the past six decades. Introduced in 1983,theinsulated-gate bipolar transistor(IGBT) has in the past two decades come to dominate VFDs as an inverter switching device. In variable-torqueapplications suited for Volts-per-Hertz (V/Hz) drive control, AC motor characteristics require that the voltage magnitude of the inverter's output to the motor be adjusted to match the required load torque in alinearV/Hz relationship. For example, for 460V, 60Hz motors, this linear V/Hz relationship is 460/60 = 7.67V/Hz. While suitable in wide-ranging applications, V/Hz control is sub-optimal in high-performance applications involving low speed or demanding, dynamic speed regulation, positioning, and reversing load requirements. Some V/Hz control drives can also operate inquadraticV/Hz mode or can even be programmed to suit special multi-point V/Hz paths. The two other drive control platforms,vector controlanddirect torque control(DTC), adjust the motor voltage magnitude, angle from reference, and frequencyso as to precisely control the motor's magnetic flux and mechanical torque.Althoughspace vectorpulse-width modulation(SVPWM) is becoming increasingly popular, sinusoidal PWM (SPWM) is the most straightforward method used to vary drives' motor voltage (or current) and frequency. With SPWM control, quasi-sinusoidal, variable-pulse-width output is constructed from intersections of a saw-toothedcarrier signalwith a modulating sinusoidal signal which is variable in operating frequency as well as in voltage (or current). Operation of the motors above rated nameplate speed (base speed) is possible, but is limited to conditions that do not require more power than the nameplate rating of the motor. This is sometimes called "field weakening" and, for ACmotors, means operating at less than rated V/Hz and aboverated nameplate speed.Permanent magnetsynchronous motors have quite limited field-weakening speed range due to the constant magnetflux linkage. Wound-rotor synchronous motors and induction motors have much wider speed range. For example, a 100HP, 460V, 60Hz, 1775RPM(4-pole) induction motor supplied with 460V, 75Hz (6.134V/Hz), would be limited to 60/75 = 80% torque at 125% speed (2218.75RPM) = 100% power.At higher speeds, the induction motor torque has to be limited further due to the lowering of the breakaway torqueof the motor. Thus, rated power can be typically produced only up to 130-150% of the rated nameplate speed. Wound-rotor synchronous motors can be run at even higher speeds. In rolling mill drives, often 200-300% of the base speed is used. The mechanical strength of the rotor limits the maximum speed of the motor.Anembeddedmicroprocessorgoverns the overall operation of the VFD controller. Basicprogrammingof the microprocessor is provided as user-inaccessiblefirmware. User programming ofdisplay, variable, and function block parameters is provided to control, protect, and monitor the VFD, motor, and driven equipment. The basic drive controller can be configured to selectively include such optional power components and accessories as follows: Connected upstream of converter --circuit breakerorfuses, isolationcontactor,EMCfilter, linereactor, passive filter Connected to DC link --braking chopper, brakingresistor

BIBILOGRAPHY

[1] G. Kaplan, Technology 1992. Industrial electronics, IEEE Spect, vol.29, pp. 4748, Jan. 1992. [2] Technology 1993. Industrial electronics, IEEE Spectr. , vol. 30,pp. 5860, Jan. 1993. [3] A. R. Al-Ali, M. M. Negm, and M. Kassas, A PLC based Power factor controller for a 3-phase induction motor, in Proc. Conf. Rec. IEEE Industry Applications, vol. 2, 2000, pp. 10651072. [4] A. Hossain and S. M. Suyut, Monitoring and controlling of a real time industrial process using dynamic model control technology, in Proc. IEEE Ind. Applicat. Soc. Workshop on Dynamic Modeling Control Applications for Industry, 1997, pp. 2025. [5] K. T. Erickson, Programmable logic controllers, IEEE Potentials, vol.15, pp. 1417, Feb/ Mar. 1996. [6] B. Maaref, S. Nasri, and P. Sicard, Communication system for industrial automation, in Proc. IEEE Int. Symp. Industrial Electronics, vol.3, 1997, pp. 12861291. [7] Mader and H. Wuper, Timed automation models for simple programmable logic controllers, in Proc. 11th Euromicro Conf. RealTime Systems, 1999, pp. 106113. [8] J. Marcos, E. Mandado, and C. M. Penalver, Implementation of fail-safe control systems using programmable logic controllers, in Proc. IEEE/IAS Int. Conf. Industrial Automation and Control, 1995,pp. 395400.

Vignan's LARA Institute of Technology & Science 25