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Feedback Controlled Brushless DC Motor Background Lecture What is a motor? A motor converts electric energy to rotating mechanical energy. Electric Energy Input voltage and current Energy Converter typical: magnetic field Rotating Mechanical Energy Output speed and torque What are motors used for? What are motors used for? Rotating action moves loads • Material-movers – Fans, pumps, conveyors, robots • People-movers – Elevators, escalators, moving walkways – Hybrid cars, buses, electric motorcycles, personal transporters (Segway) What are motors used for? Rotating action moves loads • Material-movers – Fans, pumps, conveyors, robots • People-movers – Elevators, escalators, moving walkways – Hybrid cars, buses, electric motorcycles, personal transporters (Segway) Personal Electric Vehicles New Transportation Alternative • • • • Single passenger 1-10km trips Open to weather Less-than-highway speeds up to 50km/hr • Purchase cost US$2000 up to US$100,000 PEVs Potential Impact on Society • Reduced greenhouse gas emission versus cars • Higher fuel efficiency versus cars How much CO2 comes from one gallon (6.3lbs) of automobile gasoline? • When gasoline burns, the carbon and hydrogen separate. • The hydrogen combines with oxygen to form water (H2O), and carbon combines with oxygen to form carbon dioxide (CO2). • A carbon atom has a weight of 12, and each oxygen atom has a weight of 16, giving each single molecule of CO2 an atomic weight of 44 (12 from carbon and 32 from oxygen). How much CO2 comes from one gallon (6.3lbs) of automobile gasoline? • To calculate the amount of CO2 produced from a gallon of gasoline, the weight of the carbon in the gasoline is multiplied by 44/12 or 3.7 • Since gasoline is about 87% carbon and 13% hydrogen by weight, the carbon in a gallon of gasoline weighs 5.5 pounds (6.3 lbs. x .87). • Multiply the weight of the carbon (5.5 pounds) by 3.7, which equals 20 pounds of CO2! Since PEVs are electric, do they produce CO2? • Not directly. The CO2 produced by electric power plants must be accounted for. • For the 2004 fuel mix of US electricity production, the average CO2 produced is 1.55 lbs CO2 per kWh What is CO2 production per passenger mile? • If an automobile gets 20 miles/gallon, then calculate the CO2 produced per gallon. • You will further explore this question in the assignment Barriers to PEV Adoption • New technology • Battery energy density and acquisition cost – Recent advances driven by cell phone market • Production economies • Local traffic laws • Weather inconvenience PEV Advantages Over Cars • Significantly higher fuel efficiency on a perpassenger mile basis • Significantly reduced greenhouse gas emission • Reduced congestion in high density urban areas – London, Manhattan per car entry fee • Shorter trip times in high density urban areas • Quieter Does anyone have a motor with them? What is it used for? Can we see it? Does it operate from a dc or ac power source? Motor names • (Brushed) DC motors • Brushless DC motors • AC motors – Induction motors – Synchronous motors (generators) Types of voltage inputs • DC (direct current) – Voltage does not vary with time • AC (alternating current) – Voltage changes varies over time – Typically a sinusoid, but maybe not How do motors work? One explanation: Electric current interacts with magnetic field to produce torque on a shaft Another: Two magnetic fields interact to produce torque on a shaft How does a (brushed) DC motor work? (Brushed) DC Motor from RC Car How does a brushless DC motor work? N Switch state: If magnet near coil, ON Else OFF Why doesn’t rotor stop when coil is off? BLDC you will build The components of an Aveox 36/30/1.5 brushless motor. How does the switch know if there is a magnet nearby? • Use a switch that detects a magnetic field Magnetic reed switch • Use a sensor that detects a magnetic field and commands another switch Hall-effect sensor and transistor • Use a sensor that optically detects the rotor position and commands another switch Optical encoder and transistor How does the switch know if there is a magnet nearby? • Use a switch that detects a magnetic field Magnetic reed switch • Use a sensor that detects a magnetic field and commands another switch Hall-effect sensor and transistor • Use a sensor that optically detects the rotor position and commands another switch Optical encoder and transistor How does the switch know if there is a magnet nearby? • Use a switch that detects a magnetic field Magnetic reed switch • Use a sensor that detects a magnetic field and commands another switch Hall-effect sensor and transistor • Use a sensor that optically detects the rotor position and commands another switch Optical encoder and transistor Reed Switch BLDC Schematic 1.5V 1.5V COIL l co i ed h re itc sw N 1.5V Reed switch 1.5V Reed Switch Technology Typical rating: sw 8 10 failure MTBF: mean time between failure How long will a typical reed switch last continuously operating a four pole rotor BLDC at 1000rpm? Reed Switch Technology Typical rating: sw 8 10 failure How long will a typical reed switch last continuously operating a four pole rotor BLDC at 1000rpm? rev sw 3 sw 1000 4 4 10 rev min min 8 sw min 3 min 10 failure 4 103 sw 25 10 failure (416 hours or 1.14 years) What if we want to continuously operate for more than one year? ed h re itc sw N l co i 1.5V COIL 1.5V 1.5V Reed switch 1.5V What if we want to continuously operate for more than one year? Solution: replace the reed switch with a transistor Typical transistor MTBF is >100,000’s hours (e.g., 200,000 hours or 23 years) TIP106 What are the terminals on a transistor? emitter base collector The switch is between emitter and collector. The base controls the state of the switch. Use transistor as a switch 1.5V COIL N 1.5V co i l 1.5V 1.5V TIP106 base What’s missing? Add magnetic sensor to command transistor to switch Hall-effect sensor X 3121E Where are Hall-effect sensors used (besides) BLDCs? Add magnetic sensor to command transistor to switch Hall-effect sensor X 3121E Where are Hall-effect sensors used (besides) BLDCs? Speedometers on bicycles. Why not build this circuit? 1.5V COIL Coil resistance about 4 ohms. 1.5V 1.5V 1.5V X 3121E Why not build this circuit? COIL 1.5V 1.5V 1.5V 1.5V X 3121E Coil resistance about 4 ohms. coil current V 6 1.5A R 4 Power Transistor Amplifies COIL 1.5V 1.5V 10 kW Coil circuit switched by power transistor with Hall effect sensor 1.5V TIP106 1.5V X 3121E Precision BLDC using optical encoder Optical Switch What should be the angle between one encoder tab and a rotor magnet? Optek OPB870 Optical Encoder BLDC Schematic COIL 1.5V 1.5V 10 kW Coil circuit switched by power transistor with slotted optical sensor 270 W 1.5V TIP106 1.5V OPB800 Optical switch How does a BLDC motor make a difference in PEV’s? • Higher power to weight ratio – BLDC: 2000 W/kg – Brushed DC: 1000 W/kg • Higher efficiency in converting electric energy to rotating mechanical energy – BLDC: >90% – Brushed DC: 75% • Lower maintenance – BLDC: no regular maintenance – Brushed DC: replace brushes • Lower gear-ratio transmission – BLDC: 5:1@2500rpm, typically single-stage – Brushed DC: 20:1 @10,000rpm, typically two-stage Drawbacks to BLDC versus Brushed DC • Higher acquisition cost – BLDC with electronic controller about 50% higher for 1.5hp • High magnetic field strength permanent magnets on rotor Your assignment • Build your own BLDC • Read articles: – Ulrich, “Estimating the Technology Frontier for Personal Electric Vehicles” – Heinzmann and Taylor, “The Role of the Segway Personal Transporter in Emissions Reduction and Energy Efficiency” • Discover the potential impact of PEVs on greenhouse gas emissions and fuel usage • Write a 2-3 page report on your BLDC and your discoveries