All electric machines comprise coupled electric and magnetic circuits that convert electrical energy to and/or from mechanical energy. The term electric motor tends to be used to describe the machine used in an industrial drive, regardless of whether it is converting electrical energy to mechanical motion as a motor or if it is producing electrical energy from mechanical energy as a generator. Alternative designs of motor exist, but before considering these it is helpful to consider a few basic principles of magnetic circuits and electromechanical energy conversion.

The essence of any power electronics drive is the conversion of electrical energy from one voltage and frequency to another. Many circuit topologies exist to meet different requirements. Some of the topologies are specifically associated with the control of particular motor types, while others can be used to control various forms of electrical machine. Some topologies are associated with particular applications or speed ranges.

All a.c. and d.c. drives use power semiconductor devices to convert and control electrical power. This section reviews important characteristics of the most conventional power devices in drives applications. It is common to operate semiconductor devices in switched mode operation. This mode of operation implies that the device is either fully on or fully off, and power dissipation is therefore low compared to that encountered in the linear mode of operation. It is this feature that makes switched mode operation the key to achieving high efficiency. The practically important power semiconductor devices in relation to motor drives are diodes, thyristors (also called the silicon controlled rectifier, SCR), the triode thyristors (Triac), the gate turn-off thyristors (GTO), the integrated gate commutated thyristors (IGCT), the metal-oxide semiconductor field-effect transistors (MOSFET), the insulated gate bipolar transistors (IGBT), and the bipolar junction transistors (BJT) (although this device has largely been superseded by the other devices ). Power switching devices require electronic 'gate drive' circuits for turning the device on and off. These, called 'driver circuits', are in general complex and also include protection features such as over-current protection. For this reason, details of these circuits have for the most been part limited to a description of the requirements to gate the devices.

Many applications exist where something has to be controlled to follow a reference quantity. For example, the speed of a large motor may be set from a low-power control signal. This can be achieved using a variable-speed drive. Ideally, the relationship between the reference and the motor speed should be linear, and the speed should change instantly with changes in the reference. Any control system, with an input reference signal, a transfer function F and an output. For the system to be ideal, the transfer function F would be a simple constant, so that the output would be proportional to the reference with no delay.

Different feedback devices have different features, and these should be considered when designing a system. There is often poor understanding of the characteristics of speed and position sensors and so these features are described in some detail in the following paragraphs.

The aim of many applications using variable-speed drives is to control motion. This may be simple rotary speed control of a single motor or the movement of an object through a complex profile in three dimensions involving the coordinated movement of several motors. This section focuses on the profiler and its use in single- and multi-axis systems. Rotary motion control will be used as an example unless otherwise stated, but all the principles discussed apply equally to linear motion. The function of the profiler is to take the required motion and provide appropriate speed and position references for the axis.

This section describes two ways in which this form of a.c. motor drive can decelerate a motor and its load with a simple rectifier input stage. Also described is an alternative active rectifier stage that can be used in conjunction with a voltage-source inverter to facilitate full four-quadrant operation.

Switched reluctance drive systems are of importance in some applications where high, low-speed torque is required, and less importance is placed on smoothness of rotation. Although considerable advances have been made in improving the noise characteristics of this drive, it can still be a limiting factor where a broad operating speed range is required. Stepper motors systems are somewhat in decline and would rarely be described as a general industrial drive. Their operating characteristic of being controlled by 'a computer' pulse train is now a common feature of many modern servo drives. Also, where rapid settling times are required, stepper drives, which are inherently 'open loop', are not ideal in both fundamental performance and in the respect that varying mechanical friction has a significant impact. This variability can make stepper drives unacceptable in applications where the transient performance is important.

In this section the impact drives have on the a.c. supply is considered as well as how imperfections in the supply affect the operation of drives. We shall consider power factor and explore how the use of drives requires greater precision in some of the definitions and language that have historically been used in power systems.

The control of electric motors by means of power electronic converters has a number of significant side-effects. These are primarily due to the introduction of additional frequency components into the voltage and current waveforms applied to the motor. In the case of a.c. machines, which are originally intended to operate at fixed speed, there are additional implications that need to be considered, including mechanical speed limits and the possible presence of critical speeds within the operating speed range.

This section looks at the environmental requirements, conditions and impacts that motors and drives have to operate within. Particular focus will be placed upon enclosure and the protection it affords, mounting arrangements and standards, terminal markings and direction of rotation, operating temperature, humidity and condensation, noise, vibration, altitude, storage, and corrosive gases.

Motor and drives are both, in general, highly efficient power conversion devices, but when dealing with high powers, even with high efficiency there are significant losses to be dealt with. Motor and drive designers know that thermal management is one of their most significant challenges, and significant technology is brought to bear in this area. Motor and drive designers rely on advanced thermal simulation packages in order to optimise their designs. These designs are, however, based upon defined conditions in which the equipment is expected to function. This section describes the typically available cooling arrangements for motors and the design criteria for designing drive modules into cubicles.

In applications where regenerative energy is present for significant periods of time on one or more drives it is possible to recycle this energy via the d.c. bus to another drive that is in the motoring condition.

The purpose of this section is to set out the necessary considerations for system designers and others when incorporating electronic variable-speed drives into complete machines and systems without encountering problems with electromagnetic interference, and in compliance with relevant regulations. Of necessity, only general guidelines have been provided, but because real installations have a wide variety of detailed requirements, explanation of the underlying principles is given, in order to allow the designer to cope with specific situations.

This section considers the requirements for protection of the complete drive and motor system from the effects of faults and voltage transients. As in other chapters, much of the underlying philosophy is common to all electrical power installations and it is not the purpose to repeat it here. There are some special considerations in relation to drive systems, and these are addressed. The most common form of circuit protection is the fuse, followed by various forms of circuit breaker. Standard industrial fuses and circuit breakers are designed to protect the distribution circuits from the effects both of long-term overloads and of short circuits. In the case of a circuit breaker there are separate actuators (thermal and magnetic) for these two functions, whereas the thermal design of the fuse is adjusted to effectively model the thermal behaviour of the cable in both respects. In all cases the device must also carry predictable safe peak currents such as the starting current of direct-on-line (DOL) motors without undue deterioration. It is difficult to protect semiconductor devices from damage caused by a short circuit using a circuit breaker, as the response time needs to be very rapid, so the following account refers primarily to fuses. It should be understood, however, that in some cases, especially at the lower power levels, a circuit breaker may be able to fulfil the function equally well.

Many mechanical drive trains, both fixed-speed and variable-speed, experience vibration. As operating speeds and controller performance continue to increase and motor mass and inertia fall, the danger of resonance problems increases. This subject area is complex and this description will be limited to an overview of the principles and identification of the key sources of excitation of mechanical resonances.

The installation, commissioning and maintenance of industrial power drive equipment requires careful regard to the relevant safety legislation. Industrial power supply voltages and high-speed high-torque drive systems, unless handled properly, can represent a serious safety hazard. All equipment must be used in accordance with the duty, rating and conditions for which it is designed, and particularly the power supply must be in accordance with that shown on rating plates, subject to standard tolerances. The loading and speed of the motors must not exceed those of their rating plates or any overload ratings agreed for mally with the manufacturer. No attempt should be made to open inspection apertures or similar openings, unless the motor is known to be fully isolated from the power supply and the motor cannot be rotated from the load side. All safety and protection guards and covers should be in place before motors are started.

It is not practical to describe all the characteristics for every application and/or every electrical variable-speed drive. This chapter aims to provide an insight into some of the possibilities/opportunities. Typical characteristics are covered. In order to successfully select and apply the optimum drive system, it is necessary to understand the essential features of both the alternative drive technologies and the load to be driven.

The rating of an electrical machine is usually determined by a temperature limitation, and therefore the duty cycle of the application can significantly affect the rating. There are other limits to motor capacity such as the commutation limit in a d.c. motor, and so duty cycle is not the only determinant of rating; however, if the most cost-effective motor solution is to be obtained it is always good practice to consider the duty cycle with care. IEC 60034-1 defines duty cycles and these are described in the following with a selective interpretation of their application.

The modern drive incorporates a large number of functions that were historically located in separate controllers. This trend is continuing apace with the result that there is an ever growing number of interfaces needed to the drive. It is also a sobering thought that the greatest cause of problems in many industrial plants is in the interconnecting wiring. There is clear need therefore to understand the interface types on a modern drive and how they should be used in order to ensure that the design of the system is correct. Furthermore, by understanding the different types of interface it is possible to simplify the physical interfaces by, for example, the use of a Fieldbus, and here the limitations and characteristics of such a digital communications system need to be understood if a system design is to be optimised. Finally, the growing complexity of drive functionality, including the opportunity for users to write their own functions in a drive, has led to the development of advanced PC tools for the configuration and commissioning of individual drives and drive systems as well as data logging and fault-finding capabilities. An understanding of such tools and what benefits they can bring is important to getting the most out of a modern drive.

The functions available on a modern digital drive are so numerous that only the most studious of users will be aware of the capabilities of the drive. Although many of the functions will be common across all manufacturers, some will be unique and others subtly different. Intelligent drives offer the user the opportunity to write their own specific functions that will then run on the drive. Input and output terminals on many drives will also be configurable, that is to say that the function controlled by or driving the terminals can be set by the user. It is important to note, however, that a well-designed drive will leave the factory with a default configuration that will cater for a large proportion of basic applications without the need for the user to make many or any changes to operate. Software tools are also available to guide the user through the configuration of their drive. The objective of this section is to describe in general terms the sort of functions the user may expect to find on a typical industrial drive, and what they do. In demanding applications care needs to be taken about issues such as the sample/update times of given inputs and outputs (also relevant for data communicated through serial buses). The user should consider the cost benefit of utilising such functions that exist within the drive. Less obvious is the potential improvement in performance obtained by using a function within the drive because communication time to the control loops is likely to be quicker than using an external controller. Sample and update rates must be taken into account for demanding applications. For convenience the functions have been grouped in order to illustrate the types of functions that are available and to allow the reader to readily find specific functions. The list is not exhaustive.

The core technology of motors and drives has been described in some depth. This section describes techniques that are commonly used in applications and systems in order to achieve specific system functionality such as load sharing between several motors and even tension in materials within process machinery. The functions described in this section are not specific to individual applications but find application in a broad range of applications.

Providing examples of all industrial applications of drives would be an impossible task, and provide the reader with little benefit. This section is therefore a glimpse into a small area of the drives world. Some of the most common applications have been selected, as well as some that show how drives have brought considerable benefit. Emphasis has been placed upon drive functionality and how that has an impact on the application. It is also intended to show that required functionality and indeed the vocabulary of many applications is very specialised. A good knowledge of drives is not sufficient background to be able to design a good system. Experience helps, but the optimum design results when a drives engineer who knows what a drive can do works together with a customer who knows what functionality and performance is required and what problems he would like to see solved.

The following formulae are based on the International System of Units, known as SI (Systeme Internationale d'Unites), which is used throughout this book. SI was adopted in February 1969 by a resolution of the CGPM (Conference Generale de Poids et Mesures) as ISO Recommendation R1000. A base unit exists for each of the dimensionally independent physical quantities: length, mass, time, electric current, thermodynamic temperature and luminous inten sity. The SI unit of any other quantity may be derived by appropriate simple multipli cation or division of the base units without the introduction of numerical factors. The system is independent of the effects of gravity, making a clear distinction between the mass of a body (unit of mass = kilogram) and its weight, i.e. the force due to gravity (unit of force = newton).

Provides various unit conversion tables under the headings of 'Mechanical conversion tables' and 'General conversion tables', as well as a power/torque/speed nomogram.

Data for world industrial electricity supplies are shown in a table which list the industrial three-phase supply voltages below 1 000 V and the supply frequency for various countries