Feedback Controlled Brushless DC Motor Background Lecture

What is a motor? Electric Energy Input voltage and current Rotating Mechanical Energy Output speed and torque A motor converts electric energy to rotating mechanical energy.

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 per- passenger 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? 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

Reed Switch Technology Typical rating: How long will a typical reed switch last continuously operating a four pole rotor BLDC at 1000rpm? MTBF: mean time between failure

Reed Switch Technology Typical rating: How long will a typical reed switch last continuously operating a four pole rotor BLDC at 1000rpm? (416 hours or 1.14 years)

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)

What are the terminals on a transistor? The switch is between emitter and collector. The base controls the state of the switch.

Use transistor as a switch What’s missing?

Add magnetic sensor to command transistor to switch Hall-effect sensor Where are Hall-effect sensors used (besides) BLDCs?

Add magnetic sensor to command transistor to switch Hall-effect sensor Where are Hall-effect sensors used (besides) BLDCs? Speedometers on bicycles.

Why not build this circuit? Coil resistance about 4 ohms.

Why not build this circuit? Coil resistance about 4 ohms. 3121E Hall sensor ratings

Power Transistor Amplifies Coil circuit switched by power transistor with Hall effect sensor

Precision BLDC using optical encoder Optical Switch Optek OPB870 What should be the angle between one encoder tab and a rotor magnet?

Optical Encoder BLDC Schematic Coil circuit switched by power transistor with slotted optical sensor

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: typically single-stage –Brushed DC: 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