Hand Book

Overview of Motors
and Motor Driving

Powered by

© 2022 ROHM Co., Ltd. TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

－ Table of Contents －

Introduction ....................................................................................................................................... 1

1. Motor Types and Categories ......................................................................................................... 1

2. Construction of Small Motors ........................................................................................................ 1

3. Principle of Motor Rotation ............................................................................................................ 2

3.1 About Currents, Magnetic Fields, and Forces .............................................................. 2
3.2 Principle of Motor Rotation ........................................................................................... 3

4. Power Generation Principle of Motors .......................................................................................... 4

4.1 What is Power Generation Action of Motors? .............................................................. 4
4.2 Power Generation Principle of Motors ......................................................................... 5

5. Summary of Motor Driving Systems in Various Fields .................................................................. 5

6. Four Features to Seek in a Motor Driver ...................................................................................... 7

7. Conclusion ..................................................................................................................................... 8

Revision History ................................................................................................................................ 9

Notes ............................................................................................................................................... 10

© 2022 ROHM Co., Ltd. TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

Introduction 1. Motor Types and Categories

In recent years, worldwide annual production of motors There are various approaches when considering motor
has been in the vicinity of ten billion units, and the power types and categories, and it may be that there is no
consumed by motors is said to account for roughly 50% completely objective method of categorization. However,
of total global electric power consumption. These may it is possible to classify motors according to the purpose
sound like preposterous numbers, but when one begins of use, and, from the standpoint of the user, according to
to count all the various motors one uses regularly--from the energy conversion medium, power supply,
the motors in the hard disk drives and optical drives as construction, characteristics, and so on. Taking all these
well as the cooling fans of PCs, to the many motors used factors into account, we think the categorization as shown
in washing machines, refrigerators, air conditioners, in Figure 1 is reasonable.
hybrid vehicles, and on and on--they likely begin to seem
The motors circled in red are generally referred to as
reasonable. And as one example of new measures to
small motors, and this handbook will mainly discuss them
address environmental problems, it has been expressly
with them in mind.
stated that automobiles will be electrified, primarily in
Europe and North America, so that demand for motors is ＜Summary＞
strongly trending upwards.  There are various approaches to motor types and
categories.
On the other hand, strict energy conservation regulations
have been established to address global energy issues,  From the standpoint of the users of motors, we have
and as a matter of course, energy-saving measures for presented classification examples which consider the
equipment using motors is a vital concern. In addition to energy conversion medium, power supply, construction,
energy conservation of the motors themselves, highly characteristics, and the like.
efficient motor driving and control methods are also 2. Construction of Small Motors
immensely important.
Figure 2 shows a construction overview and comparison
As explained above, motors are used in various fields and of three types of motors: general-purpose stepping
in diverse applications. Thus, there are many types of motors, brush DC (direct current) motors, and brushless
motors, and also many kinds of motor driving and control DC (direct current) motors. The basic constituent
methods. This hand book provides an overview of motor components of these motors are coils, magnets, and
fundamentals and motor drives. rotors; depending on the type, the coils may be stationary,
or the magnets may be stationary. Please understand that
this is a general structure, as there may be separate
structures in detail.

Figure 1. Motor types and categories

© 2022 ROHM Co., Ltd. -1- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

Figure 2. Example of small motor structure

In the example stepper motor, the coil is outside and fixed, The first is Ampere's right-hand thread law. It shows the
and the magnet inside rotates. relationship between the direction of the current and the
magnetic flux (see Figure 3).
In the example of a brushed DC motor, magnets are fixed
on the outside, and coils rotate on the inside. The coils
have a brush and commutator which serve to supply
current and perform switching.
In the example of a brushless motor, coils are fixed on the
outside, and magnets rotate on the inside.
Thus, although the basic components of motors are the
same, the structure differs depending on the type.
＜Summary＞
 The main basic constituent parts of a motor are coils,
permanent magnets, and rotors.
 Depending on the type, there are motors in which the
coils are stationary, and motors in which the magnets
are stationary.
3. Principle of Motor Rotation
As the foundation of motors, this section explains the
principle of motor rotation.
3.1 About Currents, Magnetic Fields, and Forces
To illustrate the principle of motor rotation, we will review
the basic physical laws and principles relating to electric Figure 3. Ampere's right-hand thread rule.
currents, magnetic fields, and forces. This material may Next is the law of magnetic flux generated in a coil by an
even evoke some nostalgia, but it is easy to forget these electric current. This is the relationship between the
laws if you don't deal with components relating to direction of the coil winding and the magnetic flux
magnetic fields on a regular basis. generated by the direction of the current (see Figure 4).

© 2022 ROHM Co., Ltd. -2- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

Figure 4. Magnetic flux generated in a coil by a current Figure 5. Fleming's left-hand rule

The last is Fleming's left-hand rule, which shows the

relationship between current, magnetic flux, and force.
The force is the value obtained by multiplying the current,
the length of the copper wire, and the magnetic flux
density (see Figure 5).
3.2 Principle of Motor Rotation
The principle of motor rotation is explained, using Figure
6 and equations.
When a conducting wire has a rectangular shape, the
forces acting on the wire are considered.
First, the force F acting on the rectangle sides a and c is

F B I l N

As a result, a torque is generated about the central axis.

Figure 6. Principle of motor rotation

© 2022 ROHM Co., Ltd. -3- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

If for example we consider a state in which the rectangle 4. Power Generation Principle of Motors
has rotated by an angle θ, the force acting
It was explained in the previous section that motors
perpendicularly on b and d is the sin θ component, and
convert electrical energy into motive power, and rotational
so the torque Ta on the side a is represented by the
motion is obtained by utilizing the forces arising from the
following equation.
interaction between magnetic fields and electrical
h currents. Conversely, mechanical energy (motion) is
Ta ≃ B I l sinθ N ∙ m converted into electrical energy by electromagnetic
2
induction. In other words, motors have an electrical
power-generating action. When we think of electric power
Treating side c similarly, overall the torque is double, and
generation, we probably imagine electric power
so the following equation is used to calculate the torque
generation equipment (also called dynamos, alternators,
generated.
generators, etc.); and indeed, these have a basic
T B I h l sinθ N ∙ m construction similar in principle to that of motors. Put
simply, by passing a current through the terminals of a
The area of the rectangle is S＝h × l, and so substitution motor, rotational motion can be obtained, and conversely,
into the above equation yields the following. when a motor is rotated about its axis, a current flows
between the terminals.
T B I S sinθ N ∙ m
4.1 What is Power Generation Action of Motors?
This equation holds not only for a rectangle, but for circles
Generation of electrical energy by a motor is due to
and other shapes in general. The electric motor is a result electromagnetic induction. Figure 7 is graphic illustrations
of application of this principle. of the related laws and action for electrical energy
generation.

Figure 7. Laws related to the power generation action of motors and the power generation action

© 2022 ROHM Co., Ltd. -4- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

The figure on the left in Figure 7 illustrates the flow of The induced electromotive force E occurring in the coil
current according to Fleming's right-hand rule. Motion of due to electromagnetic induction is as follows.
a conducting wire through magnetic flux induces an
electromotive force in the wire, causing current to flow. dϕ
E B S ω sin θ V
dt
The center and right figures illustrate Faraday's law and
Lenz's law, showing that when a magnet (magnetic flux)
The electromotive force is zero when the direction parallel
is brought close to or away from the coil, current flows in
to the coil plane is perpendicular to the magnetic flux
both cases, but the direction changes.
direction, and is the absolute maximum value when the
4.2 Power Generation Principle of Motors two are parallel.
Figure 8 and equations are used to illustrate the principle In this way, motors have an electric power generation
of motor power generation. action. What we intended to explain here is not that
motors are used for power generation, but rather that
motors have both a rotation action and a power
generation action. For generating power, a generator
(dynamo), which is optimized for power generation, is
used.
5. Summary of Motor Driving Systems in Various
Fields
The following section describes the motor drive. We
summarize the kinds of motor driving systems that are
used in different fields.
Different motor driving systems are used depending on
the field and the application. The following Table 1 and 2
provide examples together with trends in consumer
product fields and in industrial/automotive fields, to give
an idea of the kinds of motors and driving methods
actually in use.
Table 3 also shows a performance comparison of various
motors and a list of example drive control technologies.
Here a "◎" symbol in the table indicates that the motor
type is regarded as superior in the relevant respect, and
a "×" symbol indicates an inferior evaluation. These are
Figure 8. Principle of motor power generation representative examples; the number of driving elements
and other parameters differ with the motor, and there are
Suppose that a coil of area S (＝l × h) is rotating with an various methods for driving and controlling motors. These
angular velocity ω in a uniform magnetic field. comparisons can be used as reference material for
At this time, if the angle formed by the direction parallel to gaining a broad understanding of motors and motor
the coil plane (the yellow line in the center figure) and the driving.
line perpendicular to the direction of the magnetic flux
density (the black dashed line) is θ ( ＝ ωt), then the
magnetic flux φ passing through the coil is represented
by the following equation.

ϕ B S cos θ B S cos ωt

© 2022 ROHM Co., Ltd. -5- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

Table 1. Examples and Overview of Drive Systems for Home Appliances, AV, and OA Equipment

Table 2. Drive System Examples and Overview for Industrial and xEV Applications

© 2022 ROHM Co., Ltd. -6- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

Table 3. Performance comparison of various motors and drive control technologies

6. Four Features to Seek in a Motor Driver ②Low Power Consumption, High Efficiency

The following are four key points required of motor drivers In order to reduce power consumption of a motor, power
in recent years. devices and driving technology capable of low power
consumption are needed. For example, by using an
①High Reliability automatic lead angle adjustment function or the like, high
Motor drivers must be provided with functions to protect efficiency can be obtained over a broad range of rotation
motor driver ICs from abnormal voltages and currents, rates, from low- to high-speed rotation.
functions to prevent malfunctions due to power supply ③Quietness, Low Vibration
voltage drops, and other protection functions. They are
also required to secure safety through current-limiting Optimization of the driving waveform is important to
address noise and vibrations during motor operation. The
functions to control motor currents during motor startup or
forced shutdown, when being restrained, etc., as well as commutation technology that is optimal for the magnetic
functions to report fault conditions to an external host circuit of various types of motor must be used according
to the field of application, whether this is the optimal
processor or other device.

© 2022 ROHM Co., Ltd. -7- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

commutation technology (120°, 150°, sine wave) for a

brushless DC motor driver, or a soft start technique for a
fan motor driver, or a current attenuation method (decay
technique) for a stepping motor driver.
④Control and Convenience
Digital rotation control technology for motors using FLL
(frequency locked loop) and PLL (phase locked loop)
control, as well as high-precision positioning control
technologies needed for actuators, and other highly
efficient driving control algorithms are indispensable to
the development of high-performance motor applications.
There are demands for high-efficiency driving control
algorithms that can easily be utilized by designers, for
example by incorporating hard logic for control algorithms
in driver ICs. Moreover, compatibility between driver ICs
improves convenience of use. Improving convenience is
important when specification changes occur during
development, for example by enabling substitutions
without changing the PCB layout of the motor driving
control board.
7. Conclusion
As noted at the beginning of this hand book, energy
saving is an important issue for equipment using motors
in response to strict global energy saving regulations.
Therefore, in addition to improving the efficiency of the
motor itself, highly efficient motor drive and control
methods are extremely important.
This hand book provides an elementary overview of
motor principles and motor drives in anticipation of the
increasing number of beginners who will develop
equipment using motors as a part of energy saving
measures. In actual design, it is necessary to understand
the motor characteristics and specifications, select a
motor suitable for the design, determine the motor drive
method and motor drive IC, and develop software if
control by a microcontroller is required. We hope that you
will use this book as a starting point for the basics.

© 2022 ROHM Co., Ltd. -8- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

Revision History

Date Version Details

2022.3.28 001 Initial version

© 2022 ROHM Co., Ltd. -9- TWHB-11e-001

 Hand Book
Overview of Motors and Motor Driving

Notes
1. The information contained herein is subject to change without notice.
2. Before you use our Products, please contact our sales representative and verify the latest specifications.
3. Although ROHM is continuously working to improve product reliability and quality, semiconductors can break down
and malfunction due to various factors. Therefore, in order to prevent personal injury or fire arising from failure,
please take safety measures such as complying with the derating characteristics, implementing redundant and fire
prevention designs, and utilizing backups and fail-safe procedures. ROHM shall have no responsibility for any
damages arising out of the use of our Products beyond the rating specified by ROHM.
4. Examples of application circuits, circuit constants and any other information contained herein are provided only to
illustrate the standard usage and operations of the Products. The peripheral conditions must be taken into account
when designing circuits for mass production.
5. The technical information specified herein is intended only to show the typical functions of and examples of
application circuits for the Products. ROHM does not grant you, explicitly or implicitly, any license to use or exercise
intellectual property or other rights held by ROHM or any other parties. ROHM shall have no responsibility
whatsoever for any dispute arising out of the use of such technical information.
6. The Products specified in this document are not designed to be radiation tolerant.
7. For use of our Products in applications requiring a high degree of reliability (as exemplified below), please contact
and consult with a ROHM representative: transportation equipment (i.e., cars, ships, trains), primary communication
equipment, traffic lights, fire/crime prevention, safety equipment, medical systems, servers, solar cells, and power
transmission systems.
8. Do not use our Products in applications requiring extremely high reliability, such as aerospace equipment, nuclear
power control systems, and submarine repeaters.
9. ROHM shall have no responsibility for any damages or injury arising from non-compliance with the recommended
usage conditions and specifications contained herein.
10. ROHM has used reasonable care to ensure the accuracy of the information contained in this document. However,
ROHM does not warrant that such information is error-free, and ROHM shall have no responsibility for any damages
arising from any inaccuracy or misprint of such information.
11. Please use the Products in accordance with any applicable environmental laws and regulations, such as the RoHS
Directive. For more details, including RoHS compatibility, please contact a ROHM sales office. ROHM shall have
no responsibility for any damages or losses resulting non-compliance with any applicable laws or regulations.
12. When providing our Products and technologies contained in this document to other countries, you must abide by
the procedures and provisions stipulated in all applicable export laws and regulations, including without limitation
the US Export Administration Regulations and the Foreign Exchange and Foreign Trade Act.
13. This document, in part or in whole, may not be reprinted or reproduced without prior consent of ROHM.

Powered by

© 2022 ROHM Co., Ltd. - 10 - TWHB-11e-001