Variable frequency drives for industrial applications
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This document provides an overview of variable frequency drives (VFDs), including their components, operation, benefits, and applications. A VFD controls the frequency and voltage supplied to an electric motor, allowing it to run at variable speeds. It has three main sections - an input section that draws power, a rectifier that converts AC to DC, and an inverter that converts the DC back to a controlled AC waveform. VFDs provide benefits like energy savings, better process control, and protection for motors. Common industrial applications include fans, pumps, compressors, and chillers in HVAC systems.
Variable frequency drives for industrial applications
- 1. BY:NAILA SHUTTARY BRANCH:EEE ROLL NO:12D21A0213
- 2. INTRODUCTION OVERVIEW COMPARISON PURPOSE VFD OPERATION COMPONENTS OF VFD WHY USE VFD? BENEFITS OF VFD INDUSTRIAL APPLICATIONS CONCLUSION
- 3. A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. A variable frequency drive is an adjustable speed drive. VFDs are available in a number of different low and medium voltage AC-AC and DC-AC topologies. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, micro drive, and inverter.
- 4. 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 • In 1980s vector controlled semiconductor drives were introduced
- 5. Conventional electric drives (variable speed) Modern electric drives (With power electronic converters) • Bulky • Inefficient • inflexible Small Efficient Flexible
- 6. Energy savings on most pump and fan applications. Better process control and regulation. Speeding up or slowing down a machine or process. Inherent power-factor correction Emergency bypass capability Protection from overload currents Safe Acceleration
- 7. Buildings: ◦ Primarily commercial Applications: ◦ Air handling ◦ District Heating ◦ Room & Zone Operation: ◦ Control fans, pumps, compressors to reduce energy consumption
- 8. Understanding the basic principles behind VFD operation requires understanding the three basic sections of the VFD: Input section, draws AC electric power from the utility, Rectifier section, converts the AC into DC power. Inverter section, converts DC back into a controllable AC waveform.
- 9. RECTIFIER is that special type of converter that converts AC to DC
- 10. Simplified Circuit showing DC bus components The DC link is an important section of the drive as it provides much of the monitoring and protection for the drive & motor circuit.
- 11. Simplified Inverter Section of a VFD Pulse-width-modulated voltage and current waveforms
- 12. The DC waveform looks more like an AC waveform but the voltage waveform is much different. The power semi-conductors in the inverter section act as switches, switches of the DC bus, and therefore, are pulsing the motor with some voltage. A typical square wave takes its shape on the square-wave look due to this switching function ( which explains the sharp rise to peak) rather than a rotational, changing state of amplitude. This frequency and amplitude pattern is sometimes called the carrier frequency of a PWM drive. Pulse-width-modulated voltage and current waveforms Pulse- width-modulatION (PWM)
- 13. Saves energy through fan and pump speed control ◦ up to 70% energy savings in pump and fan applications e.g. 32% average savings in a ventilation system → Payback period of 1 year Decreases mechanical stress due to pressure spikes with direct on-line start & stop ◦ VFDs creates a smooth start which reduces the pressure spikes that reduce system lifetime Reduces the starting current of the motor ◦ VFDs minimize the starting current of the motor, which means electrical installation investments can be lower
- 14. As VFD usage in HVAC applications has increased, fans, pumps, air handlers, and chillers can benefit from speed control. Variable frequency drives provide the following advantages: • energy savings • low motor starting current • reduction of thermal and mechanical stresses on motors and belts during starts • simple installation • high power factor • lower KVA
- 15. Typical energy savings with VFD on centrifugal pumps Flow is proportional to speed Power varies to the cube of the speed change 20% reduction in speed = 50% reduction in energy 50% reduction in speed = 80% reduction in energy
- 16. Fans Applications (E.g.) Odor control Ventilation Cooling towers Benefits Exact air flow to match demand Energy savings (20% reduction in speed gives ~ 50% saving in energy) Constant pressure &Temperature Less wear (EG: Extends belt life) Reduced audible noise Parallel fan operation possible
- 17. Pressure Set point From The Source reservoir The VFD adjusts the pump speed based on a feedback signal from the pressure transmitter to maintain a constant pressure with changes in flow Pressure Control with VFD
- 18. INDUCTION MOTOR
- 19. Using VFDs, a small reduction in speed can save large amount of energy. They help to reduce wear and tear. This technology can meet even the most stringent harmonic standards and reduce backup sizing . They provide lower KVA,helpin alleviate voltage sags. They help to save money as well as energy losses are reduced.