ch15 - 15-1 Chapter 15 Energy Efficiency of Electric Drives...

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Unformatted text preview: 15-1 Chapter 15 Energy Efficiency of Electric Drives and Inverter-Motor Interactions Exit 2001 by N. Mohan Print TOC " ! 15-2 Energy Efficiency of Electric Drives and Inverter-Motor Interactions ! Motor Losses ! Harmonic Losses ! PPU Losses ! Efficiency of Electric Drives Exit 2001 by N. Mohan ηdrive = ηmotor x ηppu TOC " ! 15-3 Motor Losses ! Core Losses – frequency and flux density dependent (20% 25% of motor losses) •Hysteresis loss •Eddy-current loss – use laminations ! Winding Power Losses – I2R loss (55% - 60% of motor losses) ! Friction and Windage Losses (5% - 10% of motor losses) ! Stray-Load Losses (10% - 15% of motor losses) – load dependent Exit 2001 by N. Mohan TOC " ! 15-4 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 " ! 15-5 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 " ! 15-6 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 " ! 15-7 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 " ! 15-8 Economics of Energy Savings ! Present Worth value ! Payback period Exit 2001 by N. Mohan TOC " ! 15-9 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 " ! 15-10 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 premium-efficiency motors? How much more efficient are they, compared to standard motors? ! What are the effects of switching-frequency harmonics on the motor? How much should the motor be de-rated? ! What is the typical range associated with the energy efficiency of power-processing units and of overall drives? Exit 2001 by N. Mohan TOC " ! 15-11 Summary/Review ! Discuss the economics and the payback period of using premium-efficiency motors. ! Describe the various deleterious effects of PWM-inverter output voltage waveforms. Describe the techniques for mitigating these effects. Exit 2001 by N. Mohan TOC " ! ...
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