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A Unified Approach to Zero-Crossing Point
Detection of Back EMF for Brushless DC
Motor Drives without Current and Hall Sensors
研究生：陳裕仁
學號：49828011
Yen-Shin Lai and Yong-Kai Lin
IEEE TRANSACTIONS ON POWER
ELECTRONICS, VOL. 26, NO. 6, JUNE
2011
ABSTRACT
I.
II.
III.
IV.
V.
INTRODUCTION
PWM TECHNIQUES
UNIFIED BACK EMF DETECTION APPROACH
EXPERIMENTAL CONFIRMATION
CONCLUSION
2
INTRODUCTION

Brushless dc Motor (BLDCM) is with the advantages of higher power density(更高的
功率密度), no need of mechanical commutation mechanism (沒必要的機械換向), and
does not have copper losses(沒有銅損) on the rotor side.

Sensorless control is an alternative way to derive the commutation instants for
BLDCM.
無感測器控制是一種替代方法，推導出無刷直流電機的換向瞬間。

Calculate the slope of current ripple, the phase current should be detected more than
twice for each chop on or chop off period.
計算相電流的紋波電流的斜率應檢測兩倍以上在截斷器開關期間
3



The filter used to remove the high-switching-frequency noise signals caused by
pulsewidth modulation(PWM) control results in time delay and thereby deteriorating
the performance of torque response.
使用的濾波器，以除去由脈寬調製（PWM）控制的結果，在時間延遲引起的高開關頻
率的噪音信號，惡化轉矩性能。
Zero-crossing of back EMF, several independent voltage sources for detection circuit
and proper isolation mechanisms are required in this approach.
零交叉反電動勢，在這種方法中需要幾個獨立的電壓源，用於檢測電路和適當的隔離
機制。
It attracts the authors to investigate the relationship between PWM techniques and
back EMF detection methods to provide a wide range of operation speed.
PWM技術和反電動勢檢測方法，以提供廣泛的運行速度之間關係。
4
PWM TECHNIQUES 1

The high-side power device is
controlled by chopper signal every
consecutive 120° in a fundamental
period and the associated low-side
control signal is shifted by 180 °.(截斷
器控制high-side power在基本波形的每
個連續120和low-side power相關的控
制信號在180被轉移)
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PWM TECHNIQUES 2

It turns high-side power device ON
and lasts for one-sixth fundamental
period. In the following 60 °, the highside power device is controlled by
chopper signal. The same control
signal is applied to the associated lowside power device except 180 ° phase
shift.(轉至high-side power開始，並持
續為基本週期的六分之一。在60°以下
， high-side power驅動由截斷信號控
制。相同的控制信號被施加到相關聯的
low-side power驅動除了180°相移。)
6
PWM TECHNIQUES 3

The high-side power device is
chopped in one-sixth fundamental
period. In the following 60 °, the highside power device is turn ON and
clamped to the positive dc-link rail.
(high-side power驅使被截成六分之一
的基本週期。在下面的60°， high-side
power驅使是打開和箝位到正dc-link rail
。)
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PWM TECHNIQUES 4

The chop-controlled area for high-side
power device is divided into two parts,
each lasts for 30 ° The same control
signal is applied to the associated lowside power device except 180 ° phase
shift.(控制區被分為兩個部分，每個持
續時間為30°的相同控制信號被施加到
low-side power驅使相關聯，除了180°
相移。)
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PWM TECHNIQUES 5

This PWM technique is the same as
PWM technique 1. However, only
during free-wheeling period, the highside power device is clamped to
positive dc-link rail, and the low side
power device is with PWM control.
(僅在續流期間， high-side power驅使
被箝位到正的dc-link rail ， low side
power驅使是PWM控制。)
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Bootstrap:引導
Photo coupler:光電耦合器
Isolation transformer:隔離變壓器
TABLE 1
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UNIFIED BACK EMF DETECTION APPROACH




“vP ” denotes表示the terminal voltage
for the phase connected to the positive
dc-link rail during PWM control period.
“vN ” indicates the terminal voltage for
the phase connected to the negative
dc-link rail during PWM control period.
“vO ” is the terminal voltage for the
floating phase.
“PWM control” means the chopper
signal is “ON” or “OFF”. This chopper
ON period is decided by the duty(截斷
ON期間決定在功率).

“The back EMF” voltage is detected
via(通過) the terminal voltage of
floating phase.
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The following equations can be derived the back
EMF
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Back EMF and current waveforms of BLDCM.

The summation總和 of back EMF for
the phases connected to positive dclink rail and negative dc-link rail is
zero.
13

The terminal voltage of the floating
phase has either rising(上升) edge or
falling(下降) edge. For both, when the
terminal voltage becomes zero, the
zero-crossing point occurs(兩者當端電
壓變為零,過零點就會出現).
14
Terminal voltage for rising edge

5(A)“positive(正相) phase” is
connected to positive dc-link rail and
“negative(負相) phase” is connected to
negative dc-link rail.

5(B)The terminal voltage for the
floating phase is derived by (6) and
can be written as

5(C). The terminal voltage for the
floating phase is derived by (6) and
can be written as
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Terminal voltage for falling edge.

6(A) In the “Chopper ON” period for
PWM, terminal voltages Vp = (Vd c −
Ip Ron ) and Vn =Ip Ron.

6(B) Floating phase is derived by (6)
and can be written as

6(C) in the “Chopper OFF” period for PWM,
Vp = (Vd c − Ip Ron ) and Vn = (Vd c + Vd ).
The terminal voltage for the floating phase is
derived by (6) and can be written as
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TABLE2
反電動勢過零點檢測狀況
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TABLE3
PWM技術反電動勢檢測方法
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EXPERIMENTAL CONFIRMATION
The control technique includes zero-crossing point of back EMF detection,
PWM control, and duty ratio control.
(控制技術過包括過零點的反電動勢檢測, PWM control, 和功率比控制)
19

Shows the block diagram(框圖)of the
experimental system, which consists
of an FPGA controller, inverter
BLDCM, and the proposed unified
back EMF detection circuit. To confirm
the back EMF detection algorithm,
neither current nor Hall sensor is
required.
(實驗系統由FPGA控制逆變器,BLDCM
和反電動勢電流檢測,確定了反應電動勢
檢測算法不用電流和霍爾感測器)
20

For PWM 4,
反電動勢可以被檢測“Chopper ON” 情
況之下,低功率操作因此受限.相對其他
PWM techniques的馬達可以被操作功
率= 5%, 0.05 per unit (p.u.) of speed,
base speed = 2500 r/min,反電動勢可
以被檢測“Chopper OFF ”情況
21

The motor can be operate(操作), as
the duty is up to 90%, which is
approximated(近似)to 1.0–1.09 p.u. of
base speed. These results confirm(確
定) that the proposed(建議) technique
provides(提供) wide speed ranges.
馬達可以操作，功率高達90％，這近似
為1.0-1.09基本速度。這些結果證實，
所提出的技術提供了廣泛的速度範圍。
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CONCLUSION

1. 提出一個統一反電動勢檢測無位置感測器,無刷直流電動機驅動器的調速方法

2. PWM技術依賴反電動勢檢測方法

3. 反電動勢檢測方法修改包括：基準電壓和採樣時刻（Chopper ON或Chopper OFF）
的端電壓。不使用任何電流感測器和霍爾感測器的無刷直流電機驅動器,實驗結果充分
驗證了理論分析
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Thank you for your attention.