Typically Predetermined:

• Mechanical Load

  • Determined by application

  • Torque-speed requirements

  • Duty cycle

  • Environmental conditions

• Power Source

  • Determined by infrastructure

  • Grid availability

  • Voltage and frequency standards

  • Power quality

Designer Must Select:

• Electric Motor

  • Type (DC, AC, synchronous, etc.)

  • Size and ratings

  • Speed-torque characteristics

  • Efficiency and power factor

• Power Converter

  • Topology (rectifier, inverter, etc.)

  • Switching frequency

  • Ratings and protection

• Controller

  • Control algorithm

  • Sensors and feedback

  • Processing platform

Advantages:

• Excellent speed control

• High starting torque

• Simple control (before VFDs)

• Wide speed range

• Four-quadrant operation

• Fast dynamic response

Applications:

• Traction (trains, metros)

• Rolling mills

• Paper machines

• Cranes and hoists

• Machine tools (legacy)

Disadvantages:

• Commutator and brushes

• Regular maintenance needed

• Not suitable for dirty/explosive environments

• Higher cost than induction

• Limited speed (commutation)

• Sparking issues

Modern Trend:

• Being replaced by AC drives with VFDs

• BLDC motors for brush-free operation

• Still dominant in some legacy installations

Advantages:

• Robust and reliable

• Low cost and Minimal maintenance

• Suitable for harsh environments

• Self-starting

• High efficiency (\(92-96\%\))

• Available in wide power range

Types:

• Squirrel Cage: Rugged, low cost, most common

• Wound Rotor: Better starting, speed control via rotor resistance

Disadvantages:

• Poor power factor at light loads

• Limited speed control (without VFD)

• Lower starting torque (squirrel cage)

• Inrush current (\(5-7 \times\) rated)

• Requires complex control for high performance

Applications:

• Pumps and fans (60–70% of all motors)

• Compressors, Conveyors, Process industries etc.

• HVAC systems

Characteristics:

• Constant speed (synchronous with supply frequency)

• Can operate at leading, lagging, or UPF

• No slip losses and high efficiency

• Requires DC excitation or permanent magnets

Types:

• Wound Field: Adjustable excitation, large power

• Permanent Magnet (PMSM): Compact, high efficiency

Advantages:

• Power factor correction capability

• High efficiency at all loads

• Constant speed under varying loads

• Suitable for low-speed, high-torque

Applications:

• Large compressors

• Ball mills, rubber and paper mills

• Power factor improvement

• Electric vehicles (PMSM)

• Servo systems

Construction:

• Permanent magnet rotor

• Electronically commutated stator

• Hall effect sensors for position

• Requires electronic controller

Advantages:

• No brushes (maintenance-free)

• High efficiency (\(85-90\%\))

• High power density

• Low electromagnetic interference

• Long life and better heat dissipation

Disadvantages:

• Higher initial cost

• Complex control required

• Permanent magnet cost

• Limited high-temperature operation

Applications:

• Electric vehicles

• Computer hard drives

• HVAC fans

• Drones and quadcopters

• Power tools, medical equipment, aerospace actuation etc.

Single-Phase AC:

• Voltage: 120V/240V (US), 230V (Europe/India)

• Frequency: 60 Hz or 50 Hz

• Applications:

  • Residential and small commercial

  • Motors up to \(\sim\)3 kW

• Limitations:

  • Pulsating torque

  • Lower power capacity

  • Starting issues

Three-Phase AC:

• Voltage: 208V, 480V, 4160V, etc. (US)
  400V, 690V, 11kV, etc. (International)

• Frequency: 50/60 Hz standard

• Applications:

  • Industrial facilities

  • Commercial buildings

  • All power levels

• Advantages:

  • Constant power, and better efficiency

  • Self-starting motors and balanced loading

Battery Systems:

• Types: Lead-acid, Li-ion, NiMH, etc.

• Voltages: 12V, 24V, 48V (automotive)
  200–800V (EVs), 270V (aircraft)

• Applications:

  • Electric vehicles

  • Material handling (forklifts)

  • Backup power (UPS)

  • Portable equipment

Advantages:

• Energy storage

• Portable

• Clean power

Other DC Sources:

• Solar PV:

  • Variable DC output

  • Requires MPPT converter

  • Growing in solar pumping

• Fuel Cells:

  • Clean hydrogen-to-electricity

  • Limited to specialized applications

• Rectified AC:

  • Most common industrial DC

  • Controlled or uncontrolled rectification

Challenges:

• Energy density (weight)

• Charging time, Cost, and Life cycle

Typical Configuration:

• Utility connection (MV)

• Main transformer(s)

• Multiple voltage levels:

  • 11 kV or 6.6 kV distribution

  • 690V or 400V for drives

  • 230V for lighting/control

• Emergency generators

• UPS systems for critical loads

• Power factor correction

Special Systems:

• Aircraft:

  • 400 Hz, 3-phase AC

  • 270V DC bus

  • 28V DC (legacy)

• Ships:

  • 440V, 60 Hz typical

  • DC distribution for propulsion

• Railways:

  • 25 kV AC overhead (India)

  • 1500V DC or 3000V DC

• Data Centers:

  • 380V DC distribution (emerging)

  • Higher efficiency

Speed Requirements:

• Constant speed needed:

  • Synchronous motor (best)

  • Induction motor (good)

  • DC shunt with feedback

• Variable speed:

  • Induction + VFD

  • DC separately excited

  • PMSM + controller

• Positioning:

  • Servo motors (BLDC/PMSM)

  • Stepper motors

Torque Requirements:

• High starting torque:

  • DC series

  • Wound rotor induction

  • PMSM with VFD

• Constant torque load:

  • DC shunt

  • Induction + VFD

• Variable torque (fan):

  • Squirrel cage induction

  • Energy savings with VFD

Environmental Constraints:

• Clean environments:

  • Food, pharmaceutical, aerospace

  • No brushes (BLDC, induction)

  • Sealed enclosures

• Hazardous locations:

  • Explosion-proof motors

  • Special cooling

  • Intrinsically safe circuits

• Outdoor/harsh:

  • IP55/IP65 enclosures

  • Corrosion protection

  • Temperature ratings

Cost Hierarchy:

• Initial cost:

  • Lowest: Squirrel cage induction

  • Medium: DC, wound rotor

  • Highest: PMSM, servo motors

• Operating cost:

  • Energy consumption

  • Maintenance requirements

  • Downtime costs

• Life cycle cost:

  • Total cost over 10-20 years

  • Often energy dominates

  • VFD pays back quickly

Load Characteristics:

• Power \(\propto\) speed\(^3\) (fan law)

• Torque \(\propto\) speed\(^2\)

• Unidirectional

• Frequent speed changes

Power Source:

• 3-phase, 400V, 50 Hz

• Grid connected

Motor Selection:

• Best Choice: Squirrel cage induction + VFD

• Rating: Based on maximum flow requirement

• Energy class: IE3 or better

Justification:

• Lowest cost solution

• High reliability

• VFD enables huge energy savings

• Simple maintenance and Proven technology

Load Characteristics:

• Multiple axes (X, Y, Z, spindle)

• Bidirectional operation

• Precise positioning required

• Fast dynamic response

• Variable cutting loads

Power Source:

• 3-phase, 400V, 50 Hz

• Clean, stable supply

Motor Selection:

• Axes: PMSM servo motors with encoders

• Spindle: Induction motor + VFD

Justification:

• Servo motors: High precision, fast response

• Encoders: Position feedback

• Spindle: Variable speed, high power

• Four-quadrant capability

Load Characteristics:

• Constant torque (hoisting)

• Four-quadrant operation

• Regenerative braking needed

• High starting torque

• Smooth acceleration/deceleration

Requirements:

• Comfort (low jerk)

• Safety (reliable braking)

• Energy efficiency and Low noise

Motor Selection:

• Modern: PMSM gearless traction

• Traditional: Induction + gearbox + VFD

Justification:

• PMSM: Compact, efficient, gearless

• Regeneration: Returns energy to grid

• VFD: Smooth control, energy savings

• Modern trend: PMSM replacing geared systems