INTRODUCTION

2. Electrical Drives
Drives are systems employed for motion control
Require prime movers
Drives that employ electric motors as
prime movers are known as Electrical Drives

3. Electrical Drives
• About 50% of electrical energy used for drives
• Can be either used for fixed speed or variable speed
• 75% - constant speed, 25% variable speed (expanding)
• MEP 1522 will be covering variable speed drives

4. Example on VSD application
motor pump
valve
Supply
Constant speed Variable Speed Drives
Power
In
Power loss
Mainly in valve
Power out
INTRODUCTION

5. Example on VSD application
motor pump
valve
Supply
motorPEC pump
Supply
Constant speed Variable Speed Drives
Power
In
Power loss
Power out
INTRODUCTION
Power loss
Mainly in valve
Power outPower
In

6. Power loss
Mainly in valve
Power out
motor pump
valve
Supply
motorPEC pump
Supply
Constant speed Variable Speed Drives
Example on VSD application
INTRODUCTION
Power
In
Power loss
Power
In
Power out

7. Conventional electric drives (variable speed)
• Bulky
• Inefficient
• inflexible

8. Modern electric drives (With power electronic converters)
• Small
• Efficient
• Flexible

9. Modern electric drives
• Inter-disciplinary
• Several research area
• Expanding
Machine design
Speed sensorless
Machine Theory
Non-linear control
Real-time control
DSP application
PFC
Speed sensor less
Power electronic converters
Utility interface
Renewable energy

10. Components in electric drives
Motors
• DC motors - permanent magnet – wound field
• AC motors – induction, synchronous (IPMSM, SMPSM),
brushless DC
• Applications, cost, environment
Power sources
• DC – batteries, fuel cell, photovoltaic - unregulated
• AC – Single- three- phase utility, wind generator - unregulated
Power processor
• To provide a regulated power supply
• Combination of power electronic converters
•More efficient
•Flexible
•Compact
•AC-DC DC-DC DC-AC AC-AC

11. Components in electric drives
Control unit
• Complexity depends on performance requirement
• analog- noisy, inflexible, ideally has infinite bandwidth.
• digital – immune to noise, configurable, bandwidth is smaller than
the analog controller’s
• DSP/microprocessor – flexible, lower bandwidth - DSPs perform
faster operation than microprocessors (multiplication in single
cycle), can perform complex estimations

12. Overview of AC and DC drives
DC motors: Regular maintenance, heavy, expensive, speed limit
Easy control, decouple control of torque and flux
AC motors: Less maintenance, light, less expensive, high speed
Coupling between torque and flux – variable
spatial angle between rotor and stator flux

13. Overview of AC and DC drives
Before semiconductor devices were introduced (<1950)
• AC motors for fixed speed applications
• DC motors for variable speed applications
After semiconductor devices were introduced (1950s)
• Variable frequency sources available – AC motors in variable
speed applications
• Coupling between flux and torque control
• Application limited to medium performance applications –
fans, blowers, compressors – scalar control
• High performance applications dominated by DC motors –
tractions, elevators, servos, etc

14. Overview of AC and DC drives
After vector control drives were introduced (1980s)
• AC motors used in high performance applications – elevators,
tractions, servos
• AC motors favorable than DC motors – however control is
complex hence expensive
• Cost of microprocessor/semiconductors decreasing –predicted
30 years ago AC motors would take over DC motors

15. Thermal considerations
Unavoidable power losses causes temperature increase
Insulation used in the windings are classified based on the
temperature it can withstand.
Motors must be operated within the allowable maximum temperature
Sources of power losses (hence temperature increase):
- Conductor heat losses (i2
R)
- Core losses – hysteresis and eddy current
- Friction losses – bearings, brush windage

16. Thermal considerations
Electrical machines can be overloaded as long their temperature
does not exceed the temperature limit
Accurate prediction of temperature distribution in machines is
complex – hetrogeneous materials, complex geometrical shapes
Simplified assuming machine as homogeneous body

17. Torque-speed quadrant of operation
ω
T
12
3 4
T +ve
ω +ve
Pm +ve
T -ve
ω +ve
Pm -ve
T -ve
ω -ve
Pm +ve
T +ve
ω -ve
Pm -ve

18. 4-quadrant operation
ωm
Te
Te
ωm
Te
ωm
Te
ωm
ω
T
• Direction of positive (forward)
speed is arbitrary chosen
• Direction of positive torque will
produce positive (forward)
speed
Quadrant 1
Forward motoring
Quadrant 2
Forward braking
Quadrant 3
Reverse motoring
Quadrant 4
Reverse braking