With Zero Emission and Human Powered Vehicles

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1 Powering the Future With Zero Emission and Human Powered Vehicles Antoni Garcia Espinosa UPC

2 CONTROL OF BRUSHLESS PERMANENT MAGNET MACHINES (BLDC) Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

3 DC motors In DC motors, the brushes of this motor areanobvious problem; there will be friction between the brushes and the commutator, and both will gradually wear away. However, a more serious problem with this type of motor: This is that the heat associated with the losses is generated in the middle of the motor, in the rotor. If the motor could be so arranged that the heat was generated in the outer stator, that would allow the heat to be removed much more easily, and allow smaller motors. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

4 BLDC->Permanent magnet rotor within stationary windings PROS No brushes or commutator to wear out No sparks and no extra fi friction More efficient than DC motor Higher speed than DC motor Higher power density than DC motor CONS Rotor sensor OR sensorless methods needed to commutate Requires six power transistors Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

5 The rotor is made of permanent magnet and can vary from two to eight pole pairs with alternate North (N) and South (S) poles. Ferrite magnets are traditionally used to make permanent magnets. Neodymium (Nd), Samarium Cobalt (SmCo) and the alloy of Neodymium, Ferrite and Boron (NdFeB) are some examples of rare earth alloy magnets. Continuous research is going on to improve the flux density to compress the rotor further Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

6 Demagnetisation curves for a NdFeB material Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

7 Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

9 WHAT IS BACK EMF? When a BLDC motor rotates, t each winding generates a voltage known as back Electromotive Force or back EMF, which opposes the main voltage supplied to the windings according to Lenz s Law. The polarity of this back EMF is in opposite direction of the energized voltage. Back EMF depends mainly on three factors: Angular velocity of the rotor Magnetic field generated by rotor magnets The number of turns in the stator windings Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

10 Trapezoidal Back EMF Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

11 Flux-linkage of coil u1u1 as the rotor rotates 1max N B r l d N B r l 1 g and the variation with as the rotor rotates from 0 to 180º is given by 1 1 1max 2 1 d1 e1 dt d e N Bglr [ ] d d V dt Powering the Future With Zero Emission and Human Powered Vehicles Terrassa d

13 N N V r l N B e ph g 2 ] [ r l B N i W i e T P V r l B N e e e e g ph w v u ] [ 2 ] [ 2 i k T k E Nm r i l B N r l B N i e T g ph g ph ] [ l r B and N k g ph 4 Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

14 in DC motor V E R i in BLDC motor V e e R R i a T 0 1 Tstall torque The no load speed is V rad 0 k s T k i This is the torque at zero speed i stall torque stall V R stall b a b Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

17 a b c In Figure (a) the current flows in the direction that magnetises the stator so that the rotor is turned clockwise, as shown. In (b) the rotor passes between the poles of the stator, and the stator current is switched off. Momentum carries the rotor on, and in the stator coil is re-energised, but the current and hence the magnetic field, are reversed. So the rotor is pulled on round in a clockwise direction. The process continues, with the current in the stator coil alternating. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

18 a b c Obviously, the switching of the current must be synchronized with the position of the rotor. This is done using sensors. These are often Hall effect sensors that use the magnetism of the rotor to sense its position, but optical sensors are also used. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

19 The Brushless DC motor is really a DC motor constructed insideout, but without the Brushes and Commutators. The mechanical switches are replaced with transistors. The windings are moved from the armature, to the stator. The magnet is moved from the outside to become the rotor Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

20 Q1 Q3 Q5 Q4 Q6 Q2 Basically are two modes of operation: Six step commutation PWM mode to control the voltage and current Six step commutation PWM mode to control the voltage and current Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

21 Unlike a brushed DC motor, the commutation ti of a BLDC motor is controlled electronically. To rotate the BLDC motor, the stator windings should be energized in a sequence. It is important to know the rotor position in order to understand d which h winding will be energized following the energizing sequence. Rotor position is sensed using Hall effect sensors embedded into the stator. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

22 Most BLDC motors have three Hall sensors embedded into the stator on the non-driving end of the motor. Each is mounted 120-degrees or 60- degrees apart on the back of the motor. Whenever the rotor magnetic poles pass near the Hall sensors, they give a high or low signal, indicating the N or S pole is passing near the sensors. Based on the combination of these three Hall sensor signals, the exact sequence of commutation ti can be determined. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

23 Powering the Future With Zero Emission and Human Powered Vehicles Terrassa Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

24 Note: Hall Effect Theory: If an electric current carrying conductor is kept in a magnetic field, the magnetic field exerts a transverse force on the moving charge carriers which tends to push them to one side of the conductor. This is most evident in a thin flat conductor. A buildup of charge at the sides of the conductors will balance this magnetic influence, producing a measurable voltage between the two sides of the conductor. The presence of this measurable transverse voltage is called the Hall effect after E. H. Hall who discovered it in Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

25 Theory of Operation Each commutation sequence has one of the windings energized to positive power (current enters into the winding), the second winding is negative (current exits the winding) and the third is in a non-energized condition. Torque is produced because of the interaction between the magnetic field generated by the stator coils and the permanent magnets. Ideally, the peak torque occurs when these two fields are at 90º to each other and falls off as the fields move together. In order to keep the motor running, the magnetic field produced by the windings should shift position, as the rotor moves to catch up with the stator field. What is known as Six-Step Commutation defines the sequence of energizing the windings. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

26 Rotor position is 000 Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

33 Six step commutation Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

34 Six step commutation At any instant, t two switches are on, one in the upper group and another in the lower group. For example, from instant t1, Q1 and Q6 are one when the supply voltage Vd and line current Id are placed across line ab (phase a and phase b in series) so that Id is positive in phase a but negative in phase b. Then after 60º, the middle of phase a, Q6 is turned off and Q2 is turned on, but Q1 continues conduction for the full 120º angle. This switching conmutates Id from phase b to phase c while phase a continues to carry +Id. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

35 Six step commutation The switching pattern changes every 60º, indicating 6 switching modes in a full electrical cycle. The sensors dictate the switching at the precise instants of the waves. It can be seen that any instant, two phase Back EMF appear in series across the inverter input, neglecting g the resistance and inductance drops. The power flow of the machine at any instant is P=2Vc Id Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

36 Brushless DC Motor Drive with 6-pulse Operation Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

39 This example shows the similarity in characteristics between the brushless dc motor and the conventional dc motor. By changing the dc bus voltage, the motor speed can be controlled. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

40 PWM control It is possible to control the switches in PWM chopping mode for controller the voltage and current continuously at the machine terminal. The devices are turned on and turned off to control the average current and the average voltage Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

43 PWM control Here we see the individual steps in a real trapezoidal current waveform. The PWM ripple is visible when the phase is active. The rising and falling edges are sloped, giving the trapezoidal shape The amount of slope is a function of the winding inductance. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

45 Torque/Speed Characteristics It is in the parallel hybrid that there is scope for some novelty in machine design. One example is the crankshaft mounted electrical machine that is used in a number of designs, including the groundbreaking Honda Insight. Here the electrical machine, which can work as either a motor or generator, is mounted directly in line with the engine crankcase. Such machines are in most cases a type of brushless DC. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

46 E B l vel B l nº r Bln º rk E k V 2R I 2E 2R I 2k d S S Vd 2RS I 2 k Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

47 F BlInº M Fr BlInº r M b b k I M 2 k I V 2R I 2k d V I d S 2k 2 R S V M 2k d 2k 2 R S Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

48 100 kw, oil cooled BLDC motor for automotive ti application. This unit weighs just 21 kg. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

49 It is in the parallel l hybrid that t there is scope for some novelty in machine design. One example is the crankshaft mounted electrical machine that is used in a number of designs, including the groundbreaking Honda Insight. Here the electrical machine, which can work as either a motor or generator, is mounted directly in line with the engine crankcase. Such machines are in most cases a type of brushless DC. They are usually turned inside out, with the stationary coils being on the inside, and the rotor being a band of magnets moving outside the coil. Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

50 Diagram of inside out electric motor Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

53 BLDC Motor for Electric/ Hybrid Automobiles HEV Motor 42V ISG (Starter/ Generator) Scroll Compressor for HEV Diesel HEV Motor Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

54 Comparing a BLDC motor to a Brushed DC motor Powering the Future With Zero Emission and Human Powered Vehicles Terrassa

55 Comparing a BLDC motor to an inductor motor Powering the Future With Zero Emission and Human Powered Vehicles Terrassa