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Unformatted text preview: 151 Chapter 15
Energy Efficiency of Electric
Drives and InverterMotor
Interactions Exit 2001 by N. Mohan Print TOC " ! 152 Energy Efficiency of Electric
Drives and InverterMotor
Interactions
! Motor Losses
! Harmonic Losses
! PPU Losses
! Efficiency of Electric Drives Exit 2001 by N. Mohan ηdrive = ηmotor x ηppu TOC " ! 153 Motor Losses
! Core Losses – frequency and flux density dependent (20% 25% of motor losses)
•Hysteresis loss
•Eddycurrent loss – use laminations
! Winding Power Losses – I2R loss (55%  60% of motor
losses)
! Friction and Windage Losses (5%  10% of motor losses)
! StrayLoad Losses (10%  15% of motor losses) – load
dependent
Exit 2001 by N. Mohan TOC " ! 154 Motor Loss and Efficiency
Curves
100
90
4 , 000 Efficiency 80
70 3, 000 Loss (W) Power Factor 60 Total losses I 2 R loss 2, 000 Current (A)
Efficiency (%) 50
Power Factor (%)
40 Current
30
Load loss 1, 000 20 Core loss 10 Friction and windage
0 Exit 2001 by N. Mohan 40 80 Load (%) 120 0 25 50 75 Load (%) 100 125 TOC " ! 155 Premium – Efficiency Motors
100 Premium efficiency 95 Efficiency (%) 90 Standard efficiency 85 80
75
1 2 5 10 20 50 100 200 Rating (kW) ! Thinner, higher quality laminations
! Lower flux densities
! Larger conductors
Exit 2001 by N. Mohan TOC " ! 156 Switching – Frequency
Harmonics Effect on Motor
Losses
! Core losses increased
! Stator and rotor I2R losses increased
! Stray – load losses increased
! Losses 10%  20% higher
! Efficiency 1%  2% higher Exit 2001 by N. Mohan TOC " ! 157 PPU Efficiency
! Rectifier losses: 1%  2%
! Losses in switching section: 3%  4%
! Total PPU losses: 4%  6%
∴ ηppu = 94%  96% Exit 2001 by N. Mohan TOC " ! 158 Economics of Energy Savings ! Present Worth value
! Payback period Exit 2001 by N. Mohan TOC " ! 159 Deleterious Effects of PWM
Inverter Voltage Waveform on
Motor Life
! Derate motor (10%) because of increased losses
! Large dv/dt
• Insulation stress
• Shaft currents (currents through bearings) Exit 2001 by N. Mohan TOC " ! 1510 Summary/Review
! What is the definition of energy efficiency of electric drives?
! What are the various mechanisms of losses in motors, assuming
a sinusoidal excitation?
! How do the losses and the efficiency depend on motor speed,
assuming a constant torque loading?
! What are premiumefficiency motors? How much more
efficient are they, compared to standard motors?
! What are the effects of switchingfrequency harmonics on the
motor? How much should the motor be derated?
! What is the typical range associated with the energy efficiency
of powerprocessing units and of overall drives? Exit 2001 by N. Mohan TOC " ! 1511 Summary/Review
! Discuss the economics and the payback period of using
premiumefficiency motors.
! Describe the various deleterious effects of PWMinverter
output voltage waveforms. Describe the techniques for
mitigating these effects. Exit 2001 by N. Mohan TOC " ! ...
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 Fall '06
 Scalzo

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