Download Novel PWM Technique Without Causing Reversal DC

Robot and Servo Drive Lab.
Novel PWM Technique Without Causing Reversal DClink Current For Brushless DC Motor Drives With
Bootstrap Driver
Industry Applications Conference,
VOL. 3, Page. 2182~Page. 2188, October 2005,
By Yen-Shin Lai, Fu-San Shyu, and Yong-Kai Lin
Professor： Ming-Shyan Wang
Student ： Chih-Hung Wang
Department of Electrical Engineering
Southern Taiwan University of Science and Technology
2017/5/23
Outline










Abstract
Driver Circuit and PWM Techniques
PWM Techniques1
PWM Techniques2
PWM Techniques3
PWM Techniques4
Reversal DC-link Current
Novel PWM Technique without Causing Reversal DC-Link
Current
Experimental System
Experimental Results
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
2
Abstract

The speed of BLDM is controlled by the frequency and duty of
the Pulse-Width Modulation (PWM) technique, which is one of
the key technologies for the development of BLDM drives.

This paper will present a novel PWM technique for BLDM
drives with bootstrap driver circuit.

As compared with existing PWM techniques for BLDM drives
the presented technique doesn’t cause any reversal DC-link
current and thereby reducing the DC-link voltage fluctuation of
the drives.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
3
Driver Circuit and PWM Techniques

The inverter consists of MOSFET and driver circuit.There are three
types of driver circuits: photo coupler, isolation transformer, and
bootstrap circuit..

For small power applications, bootstrap driver dominates the
market for cost down consideration and requiring no extra
independent DC source.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
4
Driver Circuit and PWM Techniques


The capacitor “ Cboot ”provides a power source to high-side
driver and is charged when the low-side MOSFET is turned on.
Since no extra power source is required, the isolation circuit is
therefore no more needed.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
5
PWM Techniques1

As shown in Fig. 2 the high-side
power device is controlled by
chopper signal every consecutive
120 degrees in a fundamental
period.

The associated low-side control
signal is shifted by 180 degrees, as
compared to its high-side one, to
clamp the related inverter output to
the negative dc-link rail.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
6
PWM Techniques2

PWM technique 2 shown in Fig. 3
turns high-side power device on and
lasts for 1/6 fundamental period. In
the following 60 degrees, the highside power device is controlled by
chopper signal.

The same control signal is applied
to the associated low-side power
device except 180-degre phase shift.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
7
PWM Techniques3

For the PWM technique shown in
Fig. 4, the high-side power device
is chopped in 1/6 fundamental
period and the duty ratio is
derived from the speed reference.

Moreover, the high-side power
device is clamped to the positive
dc-link rail in the consecutive 1/6
fundamental period.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
8
PWM Techniques4

Fig. 5 shows the control signals for
PWM technique reported in [11].
The chop-controlled area for highside power device is divided into
two parts, each lasts for 30 degrees.

This division solves the circulating
current issue of the floating phase.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
9
Reversal DC-link Current

PWM technique 1 shown in Fig.
2 is very popular for low power
MOSFET-driven BLDCM
drives because the bootstrap
driver circuit can be adopted.
However, it invokes reversal
DC-link current

The current in the conducting
phase flows back to the DC link
and thereby significant DC-link
voltage fluctuation.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
10
Reversal DC-link Current


This issue occurs at the commutation instance for PWM technique
1 and 2. Fig. 7 illustrates the current path using t [0 ~ 60] as
an example.
During the first several choppers around t  [0] , the energy of
floating phase has not yet been fully released.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
W、U  W、V
11
Reversal DC-link Current
DC/ AC inverter

There is a current path between
“W” phase and “U” phase when
the high side of “W”phase is “On.
Motor
Q1
Q3
+ eu Q5
+ ev -
VDC
+ ew -

When the high side of “W” phase
is “Off” there is no current path
between “U” phase and “W”
phase, “U” phase and “V” phase.
Q2
Q4
Q6
W、U
DC/ AC inverter
Motor
Q1
Q3
+ eu Q5
+ ev -
VDC
+ ew -
2017/5/23
W = High Side Chopper On,
V = Low Side On
Q2
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
Q4
Q6
W、V
12
Reversal DC-link Current

Therefore, “U” phase discharges through DC link, and thereby
producing reversal DC-link current.
DC/ AC inverter
Motor
Q1
Q3
+ eu Q5
+ ev -
VDC
+ ew Q2
Q4
Q6
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
W = High Side Chopper Off,
V = Low Side On
13
Novel PWM Technique without Causing
Reversal DC-Link Current


Using t [0 ~ 60] as an example,
‘‘W’’ phase is clamped to positive
DC-link rail to provide a current path
for ‘‘U’’ phase to release its energy.
Therefore, there is no reversal DClink current.
This clamped period is decided by the
stored energy in the floating phase.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
14
Novel PWM Technique without Causing
Reversal DC-Link Current

The terminal voltage of floating phase is higher than VDC once
the upper free wheeling diode is flowing current.

When the floating phase releases its stored energy completely,
the terminal voltage of floating phase is lower than VDC.
DC/ AC inverter
DC/ AC inverter
Motor
Motor
Q1
Q3
+ eu -
Q1
Q5
+ ev -
VDC
Q3
+ eu Q5
+ ev -
VDC
+ ew -
+ ew Q2
Q4
WU
2017/5/23
Q6
Q2
Q4
Q6
W = High Side Chopper On,
V = Low Side On
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
15
Novel PWM Technique without Causing
Reversal DC-Link Current
DC/ AC inverter
DC/ AC inverter
Motor
Q1
Q3
Motor
+ eu Q1
Q5
+ ev -
VDC
Q3
+ eu Q5
+ ev -
VDC
+ ew Q2
Q4
Q6
W = High Side Chopper On,
V = Low Side OFF
+ ew Q2
Q4
Q6
W = High Side Chopper OFF,
V = Low Side ON
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
16
Experimental System
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
17
Experimental Results

Fig. 10 shows the experimental results for PWM technique “1”
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
18
Experimental Results

The presented PWM technique doesn’t cause any reversal DClink current as shown in Fig. 11.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
19
Experimental Results

The reversal DC-link current will cause fluctuation of DC-link
voltage.

For the same converter switching frequency, the fluctuation of DClink voltage depends upon the value of output capacitor, current
supplied by the adapter and reversal DC-link current.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
20
Experimental Results
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
21
Experimental Results
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
22
Experimental Results

From these experimental results some remarks can be derived as follows.

1. The presented PWM technique can cope with the reversal DC-link current
issue and thereby reducing the DC-link voltage fluctuation.
2. The DC-link voltage fluctuation caused by reversal DC-link current decreased
when the value of DC-link capacitor increased.
3. The DC-link voltage fluctuation caused by reversal DC-link current increased
when the load is increased.


2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
23
Conclusion

This paper contributes to the presentation of a novel PWM
technique for widely used small power brushless DC motor
drives driven by bootstrap driver circuit which has been
widely used in small power applications.

Experimental results derived from an FPGA based controller
show that the presented PWM technique can cope with the
reversal DC-link current issue and thereby reducing the DClink voltage fluctuation.
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
24
Thanks for listening!
2017/5/23
Department of Electrical Engineering
Robot and Servo Drive Lab.
Southern Taiwan University of Science and Technology
25