Electric Motors -- Fundamentals and Control (Article index + Intro)

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1.Reconsiderations of basic motor and generator action

  1. The nature of the new control techniques
  2. Action at a distance
  3. Electrostatic force
  4. Consideration of the use of magnets to achieve motor action
  5. Examples of the permanency of magnets
  6. Attempts to produce motor action from permanent magnets
  7. The electric charge situated in a magnetic field
  8. Successful demonstrations of interaction between electric charges and magnetic fields
  9. The physical deflection of current-carrying conductors
  10. The solenoid as a means of manipulating the magnetic field
  11. The iron-core solenoid
  12. Super-strong magnetic fields from air-core solenoids
  13. The controllability of coil-produced fields leads to a true motor
  14. Another source of motor action
  15. The simplest dynamo
  16. The commutator and the field poles in DC motors
  17. Motor action from the reluctance principle
  18. Electric motors at the microscopic level
  19. The ball bearing motor

2. Classic DC motors

  1. Enhanced motor action from the use of iron or other ferromagnetic materials
  2. Motor and generator action
  3. A disadvantage of the commutator
  4. Armature reaction
  5. Armature self-inductance
  6. Canceling armature reaction with compensating windings
  7. The use of interpoles to improve commutation
  8. Additional techniques for improving commutation
  9. Machine function and reversal of rotation
  10. Speed behavior of DC shunt motors
  11. Basic characteristics of the shunt motor
  12. Motor speed control by shunt field current
  13. Non-rheostat control of armature voltage
  14. The series motor
  15. The compound motor
  16. The user’s comparison of motor ratings
  17. A motor is also a generator
  18. Characteristics of the basic DC generator
  19. Some unique aspects of modern permanent-magnet motors

3. Classic AC motors

  1. Operation of the series motor from AC power
  2. Some practical aspects of AC series motors
  3. The repulsion motor
  4. The single-phase induction motor
  5. The split-phase induction motor
  6. Control features of the split-phase induction motor
  7. The capacitor-start, split-phase motor
  8. The permanent-capacitor split-phase motor
  9. The two-value capacitor motor and the autotransformer capacitor motor
  10. The shaded-pole motor
  11. The repulsion-start induction motor
  12. The repulsion-induction motor
  13. The polyphase induction motor
  14. The synchronous motor
  15. The hysteresis synchronous motor
  16. The reluctance synchronous motor
  17. The elusive aspect of the induction motor principle
  18. The asynchronous generator
  19. Regenerative braking
  20. Concatenation of induction motors
  21. The AC powered shunt motor—Where is it?

4. Electronic control of commutator-type machines

  1. Speed control of a universal motor with SCR
  2. Regulated speed control of universal motors
  3. Triac speed control for universal motors
  4. Full-wave speed control for shunt motors
  5. Feedback speed-control circuit for permanent-magnet motors
  6. Independent speed and torque control of shunt motors
  7. The torque control of DC motors
  8. Tachometer feedback system for speed control
  9. Synchronous speed control for shunt and permanent-magnet motors
  10. Pulse-width modulated motor control
  11. Motor speed control with a phase-locked loop
  12. Incremental control of DC motors
  13. The Kramer speed-control system
  14. Dynamic braking circuit for DC motors
  15. DC motor speed/position control system

5. Electronic control of non-commutator machines

  1. Triac speed-control circuit for induction motors
  2. Motor-reversing technique for garage door openers
  3. Electronic switch for the capacitor-start induction motor
  4. Brushless DC motors
  5. Triac control circuit for three-phase induction motors
  6. Variable-frequency inverter for speed control of a three-phase motor
  7. An analog three-phase generator for induction motors
  8. Logic-circuit speed controller for a permanent-capacitor, split-phase motor
  9. The Slo-Syn synchronous stepping motor
  10. Dynamic braking techniques for AC motors
  11. The electronic regulation of the automotive alternator
  12. The "future" of electronic control of non-commutator machines:
    • Pulse-width modulation systems for AC motors
    • The cycloconverter
    • SCRs with gate turn-off capability
    • Motors designed for a wide range of control
    • Smart motor controls

6. Control applications for a variety of electric motors

  1. Energy conservation via power factor control
  2. Stepper motor controller
  3. Antenna rotators
  4. Speed and direction control for DC motors
  5. Motor speed control by resistance modulation
  6. The DC regulated power supply as a motor controller
  7. Precise control of motor speed with programmable divider
  8. Constant-current motor drive
  9. The use of square waves to operate motors
  10. AC operating voltage from the Darlington inverter
  11. Pulse-width modulation in a package
  12. The LM3524 regulating pulse-width modulator IC
  13. DC motor control with the use of a pulse-width modulator IC
  14. Stepped-waveform inverter suitable for operation of motors

7. The non-classic motors

  1. The off-the-beaten-path motor concept
  2. The permanent-magnet stepping motor with unipolar drive
  3. The permanent-magnet stepping motor with bipolar drive
  4. Drive-current switching for improving speed, torque, and efficiency of stepping motors
  5. The variable-reluctance stepping motor
  6. Electronic commutation for the DC brushless motor

8. The electric automobile: pros and cons

  1. The lead-acid battery: survivalist-hardened energy source
  2. The chemical action in the lead-acid cell
  3. The nickel-iron battery: another enduring tough one
  4. Basic chemistry of the nickel-iron cell
  5. Batteries—Plain and fancy:
  6. Can the utilities handle the load imposed by electric vehicles?
  7. DC or AC motors?
  8. Reducing losses with germanium power transistor choppers
  9. Conversions: A practical path to electric propulsion
  10. The fuel cell
  11. A common sense appraisal of electric autos
  12. Cold fusion, hot debates, and tantalized electric vehicle enthusiasts
  13. “Horse energy”—food for thought

Additional, useful information

  1. Speed, slip, and frequency:
    • Speed of any DC motor-general equation
    • Speed of a given DC series motor
    • Speed of any DC series motor
    • Speed of any DC differential compound motor
    • Speed of any DC cumulative compound motor
    • Synchronous speed
    • Subsynchronous speed
    • Rotor speed of induction motor
    • Slip of rotor in an induction motor
    • Frequency of an alternator
    • Rotor frequency in an induction motor
  2. Force and torque:
    • Force exerted on an armature conductor
    • Shaft torque of motors
    • Torque developed in armature of any DC motor—general equation
    • Torque developed in armature of a given motor
  3. Polyphase relationships:
    • Relationships in two-phase motor operating from 3-wire line
    • Power delivered to three-phase motor
    • Power factor of three-phase motor
  4. Generators and alternators:
    • Generator action
    • EMF induced in a conductor cutting a magnetic field
    • Instantaneous voltage in a coil rotating in a uniform magnetic field
    • Counter EMF in DC motors
    • Effective EMF per phase in an alternator
  5. Current and magnetic field relationships:
    • Hand rule for current-carrying conductor
    • Hand rule for coils or solenoids
    • Hand rules for motors and generators
  6. Miscellaneous:
    • Efficiency of any motor
    • Current and torque relationship in motors
  7. Effective value of sine wave:
    • Voltage induced in a transformer winding
    • Field current in a DC shunt motor

Achieve maximum energy efficiency in electric motors!

This guide is perfect for anyone who works with or is interested in electric motors. This practical guide explains how different types of motors operate, and how electronic control devices can be used to improve efficiency in a wide range of applications.

This guide is continuously updated and expanded to cover state-of-the-art digital stepper motors and microprocessor controls, as well as new motor and control techniques

This guide contains in-depth coverage of:

  • DC motors
  • AC motors
  • Commutator-type motors
  • Non-commutator-type motors
  • Electric motor control applications
  • The permanent-magnet stepping motor with bipolar drive
  • The variable-reluctance stepping motor
  • Electric vehicle energy sources (including the lead-acid battery and the nickel-iron battery)

This guide also includes useful information on:

  • Generators and alternators
  • Polyphase relationships
  • Force and torque
  • Current and magnetic field relationships


From ships to toys, from steel mills to electric cars, and wherever electrical energy has teamed with mechanical motion, the impact of solid-state electronic control of electric motors has made itself felt. It’s true that antennas were rotated, tools were driven, and vehicles were electrically powered prior to the advent of thyristors, power transistors, and sophisticated integrated-circuit modules. However, the improvements in precision, flexibility, reliability, and controllability have been so great with the new devices and techniques, that we find ourselves involved with a new and fascinating aspect of technology.

Electric motors, generators, and alternators (the so-called “dynamos” of yesteryear) assumed their roles as industrial “workhorses” during the latter portion of the previous century and the early part of this century. Surprisingly, a perusal of texts dating that far back can still yield useful information about starting, stopping, reversing, and stabilizing such machines. But continued reliance on these venerable methods can only lead to technical obsolescence of machines and techniques. A new era of motor control exerts new demands and, at the same time, stimulates new challenges and provides new opportunities.

When both power engineering and electronics were still in their early stages, those with bold imaginations perceived the potential benefits that might result from a merger of the two arts. A formidable deterrent to such mutuality between these two electrical disciplines was the unreliability of then-available electronic devices and components. During the 1930 to 1950 interim, the electronic control of motors did make some headway as better tubes and components became available for such applications. In particular, thyratrons and ignitrons attained popularity. It became feasible to electronically control the speed of fractional-horsepower machines and, to some extent, larger integral-horsepower machines. Significantly, some of these circuit techniques are clearly recognizable as the predecessors of present-day solid-state controllers.

This obviously brings us to the solid-state topic of electronic evolution. Initially, the invention of the transistor sparked a number of application efforts. With the soon-to-follow development of power transistors, the direct control of larger electromagnetic devices became possible. Also, the introduction and quick commercialization of thyristors enabled the precise and efficient control of very large motors. Now, a plethora of solid-state devices have become available for arriving a wide range of motor types and sizes; these include silicon NPN and PNP power transistors, N and P channel power MOSFETs, power Darlingtons, germanium power transistors, IGBTs, GTOs, MCTs, and power op amps.

So much for the muscles for motor-control systems. Fortunately, technological- evolution has also provided us with the brains to actuate these muscles in coordinated precision. No end of dedicated ICs have been developed to time, automate, manipulate, and protect these motor-control systems. Both analog and digital techniques are used; excellent control and regulation of motor operational-parameters can be realized without extensive development-projects, or wasteful cut-and-try activities.

The motors, too, have participated in this evolution. The traditional motor-formats, although remaining useful, have to a considerable extent given way to types relying less upon mechanical commutation or conventional single or polyphase power, but much more upon timed-pulses from the alluded “brainy” control-ICs. Such motors exhibit attributes of the long-enduring DC and AC motors, but also possess unique advantages of cost, reliability, and controllability.

The foregoing matters lead very naturally to the final section of the treatise dealing with electrically-powered automobiles. Therein, weendeavor to resolve some of the controversies that have long plagued this area of electric-motor application. Interestingly, all of the preceding sections bear relevancy. The propulsion of the electric auto can be provided by DC or AC motors, and by traditional or new-age motor formats. This stems from the versatility of the aforementioned dedicated control-ICs.

Regardless of specific areas of interest, if you are technically-inclined, you should find useful guidance to practical implementations of electric motors and their control, but I hope that this guide will also stimulate rewarding, experimentation and creativity.


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