Brushless dc motor (BLDC) BLDC motor control & drives

Brushless dc motor (BLDC) BLDC motor control & drives Asst. Prof. Dr. Mongkol Konghirun Department of Electrical Engineering King Mongkut s University of Technology Thonburi

Contents Brushless dc (BLDC) motor 1. Radial flux BLDC motor 2. Axial flux BLDC motor 3. Permanent magnet 4. Magnetic design 5. Commercial products of BLDC motor 2

Contents BLDC motor control & drives 1. Overview of BLDC motor drive 2. Hall sensor 3. Unipolar & bipolar drives 4. Speed control of BLDC motor 5. Sensorless speed control of BLDC motor 3

Brushless dc Motor

Radial flux BLDC motor

Radial flux PM motor Radial flux motors have advantages relating to manufacturing and magnetic configurations. These motors are the most common type of brushless PM motor. 1. Interior-rotor surface-magnet motor 2. Interior-rotor interior-magnet motor 3. Exterior-rotor motor

Radial flux PM motor 1 Surface-magnet motor with arc magnets bonded to the rotor yoke. This drawing is similar to that of a motor with ring-arc magnets, fitting as a complete ring. 2 Surface-magnet motor with bread-loaf magnets. The magnets have profiled surface at the airgap, and are bonded to flats on the rotor yoke.

Radial flux PM motor 3 Inset magnets, developed by Sebastian & Schiferl to achieve better protection against demagnetization and a wider speed range using flux weakening. 4 Exterior-rotor motor. Popular in fan drives and disk drives, this motor also has a wide range of applications in motion control.

Radial flux PM motor 5 Spoke-type interior-magnet rotor. Developed to increase the airgap flux density by the flux concentration principle, this motor was used as an aircraft generator and in servo motors by Fanuc & Pacific Scientific. 6 The IPM or interior permanent magnet motor comes in a wide variety of shapes and sizes, and is used for applications as diverse as washing machines, compressors for air conditioner, and hybrid vehicle traction.

Axial flux BLDC motor

Axial flux PM motor Axial flux motors have a key benefit of making a flat motor with short overall length. Floppy-disk and fan drives are popular applications. Stator coils Rotor permanent magnet

Axial flux PM motor Topologies of AFPM brushless motor 1. Single sided AFPM motor - with slotted stator (Fig 1.4a) - with slotless stator - with salient-pole stator

Axial flux PM motor Topologies of AFPM brushless motor 2. Double sided AFPM motor - with internal stator - with slotted stator (Fig. 1.4b) - with slotless stator - with iron core stator - with coreless stator (Fig. 1.4d) - without both rotor and stator cores

Axial flux PM motor Topologies of AFPM brushless motor 2. Double sided AFPM motor - with internal stator - with salient-pole stator (Fig. 1.5)

Axial flux PM motor Topologies of AFPM brushless motor 2. Double sided AFPM motor - with internal rotor - with slotted stator (Fig. 1.4c) - with slotless stator - with salient pole stator (Fig. 1.6)

Axial flux PM motor Topologies of AFPM brushless motor 3. Multi-stage (multidisc) AFPM motor (Fig. 1.7)

Brushless DC & Brushless AC Brushless DC usually refers to the original brushless permanent-magnet motor that uses electronic commutation of an essentially direct (squarewave) current with low resolution shaft position sensors to synchronize the switching of the driving transistors with the rotor position. Brushless AC and PM AC synchronous usually refer to systems with sinewave drive.

Permanent magnet

Demagnetization curves for some PM materials S.I. C.G.S Intersection of y-axis : Residual or remanent flux density, Br (1 Tesla = 1, Gauss) Intersection of x-axis : Coercive force, Hc (1 MA/m = 4*1 koersted)

Unit conversion table

Demagnetization curve from Hitachi metals : HS-4 DH

Isoptropic & Anisotropic Magnets Isoptropic Magnets have magnetic domains that are randomly orientated and therefore they can be magnetized equally in any direction. Only the magnetic domains that lie in the particular direction of magnetization can be used. Anisotropic Magnets have their magnetic domains locked in one particular direction during manufacture. They can ONLY be magnetized along this axis. Anisotropic magnets are much stronger than isotropic magnets because all the magnetic domains are used in the same direction.

Permanent magnet shape & size (Hitachi metals)

Permanent magnet info from Hitachi metals

Cogging torque info from Hitachi metals Cogging torque is a fluctuation of torque produced when the rotor is rotated in the energized state. The cogging torque is heavily affected by variations in the manufacture of magnetic rotors.

Cogging torque reduction methods T cog 1 2 2 g dr d where g is the air-gap flux, R is the air gap reluctance and θ is the rotor position Cogging torque waveforms with air-gap length.5mm and.8mm

Cogging torque reduction methods T cog 1 2 2 g dr d where g is the air-gap flux, R is the air gap reluctance and θ is the rotor position Cogging torque waveforms among three magnet types

Cogging torque reduction methods T cog 1 2 2 g dr d where g is the air-gap flux, R is the air gap reluctance and θ is the rotor position Cogging torque waveforms with slot opening of 2 mm and 1 mm

Cogging torque reduction methods T cog 1 2 2 g dr d where g is the air-gap flux, R is the air gap reluctance and θ is the rotor position Cogging torque waveforms with 24-slots and 36-slots

Magnetic design

Magnetic design by simple C- core structure g Simple C-core structure Magnetic circuit of the C-core structure Ampere s Law l H l H NI g g m m dc L g g m g f LKG Leakage coefficient Permeance coefficient (PC) m g g LKG dc o m g m m g LKG o m A A l f NI H l l A A f B

Effect of stator slotting of BLDC motor m g g LKG dc o m g m m g LKG o m A A l f NI H l l A A f B ' g LKG dc o m ' g m LKG o m l f NI H l l f B is determined by Carter s coefficient g ' g l l g A m A ' l g (For C.G.S. unit, o = 1)

Movement of load line when air gap increases

Movement of load line when PM thickness increases

Movement of load line when NI increases

Commercial products of BLDC motor

Mitsubishi - Inverter pump

Hitachi - Inverter pump

GE fan & blower (Regal-Beloit)

GE fan & blower (Regal-Beloit) 12-pole BLDC motor (4 poles/segment)

BLDC motor (Reliance Electric)

Fasco pool pump (impower)

BLDC motor control & drives

Overview of BLDC motor drive

Basics : structure Rotor Permanent magnet rotor ABC Hall A Hall B Hall C 5 V GND Three-phase stator winding Stator Hall element sensors

Basics : structure

Is the brushless DC motor really a DC motor? V I T e

Comparison with the brushed dc motor Brushed DC motor Brushless DC motor Mechanical structure Distinctive features Winding connection Commutation method Detecting method of rotor position Reverse method Field magnet on the stator Quick response and excellent control ability Field magnet on the rotor Long-lasting, easy maintenance (usually no maintain required) Ring connection thru brush or Y connected three phase windings Mechanical contact between brushes and commutator Automatically detected by brushes By a reverse of terminal voltage Electronics switches using controllable switching devices Hall element, optical encoder Rearranging commutation sequence

Generation of trapezoidal back EMF ee e 1 2 e ( ) ( Positive polarity of e is direction of vector ( ) ) when then e 1 2 2 ee e

4-pole machine (2 coils per phase) 3 m m

4-pole machine (2 coils per phase) ( m/ s) e2 n m 3 m m m m m 9 m 18 m 27 m m 36 m

4-pole machine (2 coils per phase) 3 m m

Hall sensor

Hall element sensor Semiconductor plate N Hall IC Bias (control) current N S N Permanent magnet Generated Hall voltage

Hall element sensor

Hall sensor installation

Unipolar & bipolar drives

Electronic commutation method using chopper (unipolar driven) Three-phase BLDC Free-wheeling diode (active when switch is off)

Electronic commutation method using chopper (unipolar driven) HALL A S Permanent magnet N S1 S2 S3 I ave = (Ip)/3 =.33I p Phase A Permanent magnet S N S1 S2 S3 Ea Ia HALL B Phase B Eb Ib HALL C Phase C Ec Ic 1period 1period

Electronic commutation method using inverter (bipolar driven) Advantages (compared with unipolar): 1. Lower torque ripple 2. Higher torque (I rms > I ave ) 3. Higher efficiency Idc + Vdc - DC/AC 3-ph Inverter Q1 Controller Q6 HALL A HALL B HALL C BLDC T e m T l

Electronic commutation method using inverter (bipolar driven) Permanent magnet I rms = I p.sqrt(2/3) =.81I p S N S1 S2 S3 S4 S5 S6 Idc DC-bus BLDC Phase A Ea Ia + Vdc - Va Q1 Q3 Q5 Vb Vc Q2 Q4 Q6 Ia Ib Ic R L + - e - L + R e - + e L R Phase B Eb Ib Voltage Source Inverter Phase C Ec Ic 1period

Electronic commutation method using inverter (bipolar driven) S Permanent magnet S1 S2 S3 S4 S5 S6 N HALL A Idc DC-bus BLDC + Vdc - Va Q1 Q3 Q5 Vb Vc Q2 Q4 Q6 Ia Ib Ic R L + - e - L + R e - + e L R HALL B Voltage Source Inverter HALL C 1period

Electronic commutation method using inverter (bipolar driven) Permanent magnet Idc + Vdc - Va DC-bus Q1 Q3 Q5 Vb Vc Q2 Q4 Q6 Ia Ib Ic BLDC R L + - e - e + - e L + R L R Q1 Q3 S S1 S2 S3 S4 S5 S6 N Duty cycle = Q1,Q3,Q5 Voltage Source Inverter s t on T s f 12 khz Q5 Q2 Q4 T s t on 1 f t Q6 1period

Electronic commutation method using inverter (bipolar driven) 1 Q1 S Permanent magnet S1 S2 S3 S4 S5 S6 N Q3 Q5 2 Q2 Q4 Q6 1period

Electronic commutation method using inverter (bipolar driven) 1 Q1 Permanent magnet S N S1 S2 S3 S4 S5 S6 Q3 Q5 2 Q2 Q4 Q6 1period

Electronic commutation method using inverter (bipolar driven) 1 Q1 S Permanent magnet S1 S2 S3 S4 S5 S6 N Q3 Q5 2 Q2 Q4 Q6 1period

Speed control of BLDC motor

Speed closed-loop control drive of BLDC (without current loop) DC supply voltage * + - PI duty cycle PWM driver Q 1 VSI Q 6 Speed calculation Commutation state computation HALL A HALL B HALL C BLDC Digital signal processor

Speed closed-loop control drive of BLDC (with current loop) *

Speed calculation based on the measured rotor position Speed can be calculated by the inverse of period. In this case, 6 stages per revolution, f = 1/T = 1/(6T 1 ) Hz

Sensorless speed control of BLDC motor

Sensorless drive of brushless DC motor

Sensorless speed control of brushless DC motor drive *

Commutation state estimation based on zero-crossing of back EMF -- Typically, the rotor position or back EMF in each state (S1-S6) is obtained by three Hall sensors. -- The commutation state is estimated by calculating zero crossing of trapezoidal back EMFs. -- Three terminal inverter voltages are measured and used to calculate the zero-crossings of back EMFs.

Brushless dc motor (BLDC) BLDC motor control & drives Asst. Prof. Dr. Mongkol Konghirun Department of Electrical Engineering King Mongkut s University of Technology Thonburi