영구자석 재료 특성 : BH curve

BLDCM and SRM

영구자석 재료

n 분류

n 화학적 조성에 따라

: ceramics (or ferrite)

: Alnicos

: rare earth magnets

n Ferrite : electrical, thermal insulator

나머지 : metalic conductor

n Alnico : Br-high, Hc-low

ceramics : Br-low, Hc-high

rare earth : Br-high, Hc-high

n ceramics : very cheap

rare earth-cobalt (samarium cobalt) : cobalt 사용

ceramic & rare earth-ferrite (Nd-Fe-B) : non-cobalt

영구자석 재료

n 특성n Maximum energy product : (BH)max

n 온도특성

: 온도 증가시 자가특성 약화 ~ reversible or irreversible

: Br과 Hc의 온도에 대한 reversible 변화율 ~

: Nd-Fe-B : 온도에 취약, high , 140℃ 이하에서 사용

ba ,ba ,

영구자석 재료

n Nd-Fe-B magnet의 영향: 기존 영구자석 대체

: 기존 전자석 대체

: 기존 영구자석이 사용되지 않던 신영역 확대

n SmCo : Nd-Fe-B와 자기적 특성 유사

: 높은 온도에서 high demagnetization field 존재시 우수

n Ceramics : 가격대 magnet energy 비율 - 최소

: low volume, weight 요구시 Nd-Fe-B로 대체

n Alnico : low (온도 변화율) – 계측기 적용

: higher cost than Nd-Fe-B

a

BLDC Motor

n A brushless DC (BLDC) motor

n stator : a classic three-phase stator like that of an induction motor

n rotor : surface-mounted permanent magnets

n BLDC motor

: equivalent to a reversed DC commutator motor

: magnet rotates while the conductors remain stationary

n current commutation

: DC commutator motor ; by commutator and brushes

: brushless DC motor ; by power transistors switching

in synchronization with the rotor position

BLDC Motor

n position sensing of BLDC motor

: either internal or external position sensors to sense

the actual rotor position

: position can be detected without sensors.

: permanent magnet synchronous motor

n BLDC motor driving

: by rectangular voltage strokes coupled with the given rotor position

: stator flux interacts with the rotor flux for the torque and speed

: voltage strokes to be properly applied to the two phases of

the three-phase winding system so that the angle between the stator flux and the rotor flux is kept close to 90° to get the maximum generated torque

BLDC Motor

n Key Characteristicsn Really a multi-phase AC motor, but can control it like a DC motor

using trick

n Like a DC motor turned inside out, commutation done on windings

n Medium construction complexity, multiple fields, delicate magnets

n High reliability (no brush wear), even at very high achievable speeds

n High efficiency

n Low EMI

n Driven by multi-phase Inverter controllers

n Sensorless speed control possible

n Higher total system cost than for DC motors

BLDC Motor

n Application Parameters n 산업용(industrial) : voltage, motor power, speed range

n 자동차용(automotive) : voltage, motor power, speed range

n Applications

n PC fans

n Blowers n Blowers

n Washing machines

n Electrical power steering

n Industrial drive

n Servo drives

n Electric vehicle traction drive

n Automotive applications

n Refrigerator

n Air conditioning

BLDC Motor

BLDC Motor 구동원리

n Three-phase unipolar-driven BLDCM

n position detector : photo-transistor

n switching sequence와 stator magnetic field

n Three-phase bipolar-driven BLDCM

n 3상 bridge circuit 구동

n 효율 : unipolar 보다 우수: 각 권선에 AC motor 처럼 교류전류 흐름

n DC motor와 BLDC motor의 비교

Table 4.2. Comparison of conventional and brushless DC motors

Conventional motors Brushless motors

Mechanical structure Field magnets on the statorField magnets on the rotor

Similar to AC synchronous motor

Distinctive featuresQuick response and excellent controllability

Long-lasting

Easy maintenance

(usually no maintenance required)(usually no maintenance required)

Winding connectionsRing connection

The simplest : ∆ connection

The highest grad: ∆ or Y-connected three-phase connection

Normal: Y-connected three-phase winding with grounded neutral point, or four-phase connection

The simplest: Two-phase connection

Commutation methodMechanical contact between brushes and commutator

Electronic switching using transistors

Detecting method of rotor’s position

Automatically detected by brushes Hall element, optical encoder, etc.

Reversing method By a reverse of terminal voltage Rearranging logic sequencer

n rotor 위치 detecting: sensor 종류 – Hall elements

- photo-transistor- inductor sensitive to induction variation

: Hall elements

constantHall:

1

H

HCH

R

RBId

V =

n Hall 소자의 BLDCM 적용

n Hall 소자를 적용한 three-phase unipolar motor

DC motor와 BLDC motor

n BLDC motor의 형태

n Transistor inverter circuit for 3- BLDCMf

n Interior-rotor motor

BLDCM과 induction motor

n Exterior-rotor motors

n pancake or disk-type BLDCM

n 속도 제어 drive system의 구조

brushless dc motor의 진화

SRM (switched reluctance motor)

: “a statically commutated doubly-salient variable reluctance motor”

SRM

n SRM과 variable reluctance stepper motor

- SMR

: rotor-position feedback to synchronize

the commutation of the phase current

: efficient conversion of power up to 300kW

- VR stepper motor

: open-loop ~ without rotor-position feedback

: step-integrity rather than efficient energy conversion

SRM

n VR stepper motor의 구조

SRM과 BLDCM의 비교

S R Motor B L D C Motor

구조

-회전자:권선,영구자석 불필용 -회전자 : 영구자석필요-회전자 :위치검출 센서 필요 -회전자 :위치검출 센서 필요-고정자 :집중권 -고정자에분포권

-전류방향과무관

driver

기타

-다양한 inverter 형태구성가능 - Bridge 형태의 inverter

- motor와 inverter의결합기술개발중(진동,소음 과다)

-제어용등,고가

- PWM, advance 각변화로속도, 토크 제어

- PWM, flux weakening으로속도, 토크 제어

-적용초기단계 -적용성숙단계

- Short Through Fault에대한신뢰성 -모듈형태의파워소자많음

-전류방향과무관 -전류방향고려