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chapter 1 - 1-1 Chapter 1 Introduction to Electric Drive...

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Unformatted text preview: 1-1 Chapter 1 Introduction to Electric Drive Systems Exit 2001 by N. Mohan Print TOC " ! 1-2 History ❏ Constant frequency AC - essentially constant pump speed ❏ Inefficient - Heat generated in pump and throttling valve ❏ Not amenable to automation Throttling Valve Outlet MOTOR Inlet Constant frequency AC Exit 2001 by N. Mohan ⇒ Essentially Constant Speed Pump TOC " ! 1-3 Trend : Adjustable Speed Drives (ASDs) Outlet Adjustable Speed Drive (ASD) Constant frequency AC Inlet Adjustable frequency electric converter Adjustable Pump speed ❏ Driven at appropriate speed x High Efficiency Exit 2001 by N. Mohan TOC " ! 1-4 What is an Electric-Motor Drive? Electric Drive fixed form Power Processing Unit (PPU) Motor speed / position adjustable form Electric Source (utility) Load Sensors measured speed/ position Controller Power Signal input command (speed / position) ! Role of Electric Drive: Efficient conversion of power from electrical to mechanical ! Role of PPU: Delivers appropriate form of frequency to motor (as required by the load) Exit 2001 by N. Mohan TOC " ! 1-5 World Market and Scope ! healthy growth rate ~ 25% per year Exit 2001 by N. Mohan ! A very wide range of speed and power TOC " ! 1-6 Factors for Growth ❏ Technical Advances in x Linear ICs and Digital Signal Processors x Power devices ❏ Market Needs x $20 Billion market in 1997 x 25% Growth rate Exit 2001 by N. Mohan TOC " ! 1-7 Typical Applications ❏ Process Industry - agitators, pumps, fans, compressors ❏ Machining - planers, winches, calendars, chippers, drill presses, sanders, extruders, grinders, mills, presses ❏ Heating and Air Conditioning - blowers, compressors ❏ Paper and Steel Industry - hoists, rollers ❏ Transportation - elevators, trains, automobiles ❏ Textile - looms ❏ Packaging - shears ❏ Food - conveyors, fans ❏ Oil, Gas , Mining - compressors, pumps, cranes, shovels ❏ Residential - heat pumps, freezers, washing machines Exit 2001 by N. Mohan TOC " ! 1-8 Application for Energy Conservation ❏ Heat Pumps and air-conditioners - cycled operation ideal loss actual Compressor Output t ON OFF ! 30% improvement in efficiency by running compressor at appropriately reduced speed using an ASD Exit 2001 by N. Mohan TOC " ! 1-9 Energy Conservation in Pumps throttling valve Pressure (H) outlet Q2 ∆H H 2 + ∆H motor A ( H 2 + ∆ H , Q2 ) ( H 1 , Q1 ) H2 Q2 full speed inlet pump pump C ( H 2 , Q2 ) Pump curve at reduced speed Q2 Pressure across throttling valve, ∆H Unthrottled System Curve H2 reduced speed Pump curve at full speed B Throttled System Curve outlet no throttling valve Adjustable Speed Drive (ASD) D inlet Q2 0 Q2 Q1 Flow Rate (Q) x Throttling introduces extra pressure drop, ∆H x ASD reduces pump speed to match load requirement Exit 2001 by N. Mohan TOC " ! 1-10 Energy Conservation in Blower Systems Outlet damper 100 80 Power Consumption (% of full flow rate) Inlet vane 60 40 Electric drive 20 0 100 90 80 70 60 50 40 30 % Flow Rate ❏ Relative power consumption using three methods to reduce blower flow rate Exit 2001 by N. Mohan TOC " ! 1-11 Harnessing Wind Energy Variable wind Variable speed Variable speed generator Variable Frequency AC Power Processing Unit Constant frequency AC Utility Wind turbine Exit 2001 by N. Mohan TOC " ! 1-12 Hybrid Electric Vehicles IC Engine Continuously Variable Transmission Electric Motor Exit 2001 by N. Mohan TOC " ! 1-13 Multi-disciplinary Nature of Electric Drives Machine Theory Utility Interaction Electric Drives Sensors Mechanical system modelling Exit 2001 by N. Mohan Power Electronics Control Theory Real-time DSP control TOC " ! 1-14 Evolution of Power Processing Unit 200 100 Size (volum e) 60 Weight 40 20 150 Com ponents 100 Functions 50 Year 1998 1998 1993 1988 1988 1968 1983 0 0 1968 % 80 Relative unit 120 Year 4kW Danfoss VLTR power processing unit Exit 2001 by N. Mohan TOC " ! 1-15 Summary • What is an electric drive? Draw the block diagram and explain the roles of its various components. • What has been the traditional approach to controlling flow rate in the process industry? • What are the major disadvantages which can be overcome by using adjustable speed drives? • What are the factors responsible for the growth of the adjustable-speed drive market? • How does an air conditioner work? (Consult a handbook such as [10].) • How does a heat pump work? • How do ASDs save energy in air conditioning and heat pump systems? Exit TOC " 2001 by N. Mohan ! 1-16 Summary ❏ What is the role of ASDs in industrial systems? ❏ There are proposals to store energy in flywheels for load leveling in utility systems. During the off-peak period for energy demand at night, these flywheels are charged to high speeds. At peak periods during the day, this energy is supplied back to the utility. How would ASDs play a role in this scheme? ❏ What is the role of electric drives in electric transportation systems of various types? ❏ List a few specific examples from the applications mentioned in section 1-4 that you are personally familiar with. ❏ What are the different disciplines that make up the study and design of electric-drive systems? Exit 2001 by N. Mohan TOC " ! ...
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