Transcript electric drives - Techno Materials

ELECTRIC DRIVES
INTRODUCTION TO ELECTRIC DRIVES
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
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)
CONTENT
•
Power electronic system
•
Modern electric drives
•
Power electronic converter in electric drives
Modern electric drives (With power electronic converters)
•
Small
•
Efficient
•
Flexible
Components in electric drives
Motors
• DC motors - permanent magnet – wound field
• AC motors – induction, synchronous (IPMSM, SMPSM),
brushless DC
• Applications, cost, environment
• Natural speed-torque characteristic is not compatible with load
requirements
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
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
• Electrical isolation between control circuit and power circuit is
needed:
• Malfuction in power circuit may damage control circuit
• Safety for the operator
• Avoid conduction of harmonic to control circuit
Components in electric drives
Sensors
• Sensors (voltage, current, speed or torque) is normally
required for closed-loop operation or protection
• Electrical isolation between sensors and control circuit is
needed for the reasons previously explained
• The term ‘sensorless drives’ is normally referred to the
drive system where the speed is estimated rather than
measured.
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
Torque-speed quadrant of operation

T -ve
 +ve
Pm -ve
2
1
T +ve
 +ve
Pm +ve
T
3
T -ve
 -ve
Pm +ve
4
T +ve
 -ve
Pm -ve
• Quadrant of operation is
defined by the speed and
torque of the motor
• Most rotating electrical
machines can operate in 4
quadrants
• Not all converters can
operate in 4 quadrants
Torque-speed quadrant of operation

Te
m
Te
Quadrant 2
Forward braking
m
Quadrant 1
Forward motoring
T
Te
Te
m
Quadrant 3
Reverse motoring
m
Quadrant 4
Reverse braking
• Quadrant of operation is
defined by the speed and
torque of the motor
• Most rotating electrical
machines can operate in 4
quadrants
• Not all converters can
operate in 4 quadrants
Load steady state torque-speed characteristic
Hoist drive
Speed
Torque
Gravitational torque